The celestial spectacle is the second solar eclipse visible from northern Australia in six months. In November, a total solar eclipse plunged the country's northeast into darkness, delighting astronomers and tourists who flocked to the region from across the globe to witness it.

An annular eclipse is not considered as scientifically important or dramatic as a total eclipse. The moon is farther from Earth and cannot completely black out the sun, so instead of seeming to turn day into night, an annular eclipse just dims the sunlight.

"A total eclipse is overall far more spectacular, far more emotional," said Andrew Jacob, an astronomer at Sydney Observatory. Still, he said, Friday's eclipse "will give you a nice ring of sunlight in the sky it will be quite different."

At remote outposts across Australia, scientists and spectators gathered to watch as the eclipse began casting its approximately 200-kilometer-wide (120-mile-wide) shadow at dawn over Western Australia, before moving east through the Northern Territory and the top of Queensland state. The shadow was drifting across Papua New Guinea, the Solomon Islands and the tiny island nation of Kiribati, and will eventually end in a largely uninhabited area of the Pacific Ocean.

The eclipse lasted between three and six minutes, depending on its location, and blacked out around 95 percent of the sun at its peak. A partial eclipse was visible in other parts of Australia, Indonesia, New Zealand and the South Pacific.

U.S. astronomer Jay Pasachoff, who traveled to Australia to view his 57th solar eclipse, drove to a remote hill in the Outback about 50 kilometers (30 miles) north of the Northern Territory town of Tennant Creek, where he and around 100 others enjoyed one of the best and longest views of the eclipse in Australia.

Amateur astronomers clicked away on cameras and local high school students measured the drop in temperature as the moon moved in front of the sun and blocked out much of the light. The moment was magical, Pasachoff said.

"The color of the light changes in an eerie fashion, and you sense that something very strange and weird and wonderful is going on," said Pasachoff, an astronomy professor at Williams College in Massachusetts.

TORONTO (Reuters) - David scored in overtime to complete a hat trick that gave the Boston Bruins a 4-3 win over the Toronto Maple Leafs on Wednesday and a commanding lead in their playoff series.

the Maple Leafs, back in the postseason for the first time in nine years, are now staring at an early playoff exit as they trail the best-of-seven first-round series 3-1 with Game Five set for Boston on Friday.

Krejci's third goal left a capacity crowd at the Air Canada Centre stunned in disbelief after the Maple Leafs had largely controlled play during a thrilling overtime that was played at furious pace.

Breaking in on a two-on-one with Milan Lucic, Krejci picked the short side on Toronto netminder James Reimer for his fifth of the playoffs 13 minutes into overtime.

"I was looking to pass the whole way but Lucic is a lefty and he was on his backhand so that kind of made my decision a little easier," Krejci told reporters.

"I also had (Zdeno Chara), I was really thinking about leaving it for him for a one-timer because he's got the best one-timer in the league but they took him away at the last second so I just tried to shoot it.

"In overtime there is never a bad shot. It wasn't a perfect shot but it went in."

Toronto had jumped out to 2-0 lead in the first period on goals from Joffrey Lupul and Cody Franson before Boston stormed back with second period tallies from Patrice Bergeron and a pair from Krejci to move in front 3-2.

But the Boston lead lasted all of 44 seconds before Clarke MacArthur answered for the Maple Leafs when he slammed home a big rebound past Tuukka Rask.

Toronto had a glorious chance to regain control of the contest when they were handed a two-man advantage for the final 41 seconds of the period but could not find the back of the net.

In the third period it was Boston's chance to retake the lead when Toronto's Nazem Kadri was given four-minute penalty for high-sticking Chris Kelly in the face but Toronto killed off the man-advantage bringing the capacity crowd at the Air Canada Centre to its feet.

Neither team could find the back of the net during an edge-of-your-seat third period that sent the contest to overtime.

"It feels like a dagger after the effort that was put forth by our group," said Toronto coach Randy Carlyle. "It was a man's hockey game out there. There was a lot of energy, a lot of physical play but that's the way the playoffs are played."

(Editing by Frank Pingue)

PARIS (AP) -- Bye, New York! Ciao, Milan! And bonjour, Paris.

The world's largest traveling circus of fashion editors, models, buyers and journalists has descended on the French capital, clutching their metro maps and city guides, to cap fashion season for nine days of intensive ready-to-wear.

And this fall-winter 2013-14 is the biggest to date, with some 99 "on-calendar" shows that see the week almost tearing at the seams, starting earlier and finishing later than ever.

"There are 12 shows a day. Twenty-two different nationalities this season. With new top designers at work," says Didier Grumbach, president of the French Fashion Federation. "It's an impressive mix, an energy that sets Paris apart from what's going on elsewhere."

Tuesday day one saw collections dominated by three up-and-coming Belgian designers: Veronique Branquinho, Cedric Charlier and Anthony Vaccarello, who dressed actress Charlotte Gainsbourg at last Friday's Cesar film awards.

The similarities start and end with their nationalities; all three threw together strong but highly individual collections.

If Branquinho was elegance, Charlier was edgy architecture, and Vaccarello was retro sex-appeal.

In other shows of the day, Le Moine Tricote spiced up the bread-and-butter knitwear with woven fabric.

Wednesday's shows include Guy Laroche, Damir Doma and London's enfant terrible, Gareth Pugh.

ANTHONY VACCARELLO

The no-holds-barred sex appeal for Anthony Vaccarello is not for the faint-hearted.

The third Belgian designer to show on Paris fashion week's first day served up a black-and-white ode to the early '80s in a show that featured micro skirts, chainmail, a lot of skin and lashings of sensual leather.

Strong retro shoulders, asymmetrical, diagonally cut skirts, upturned lapels and cowl collars set the fashion time dial firmly back to the era of the New Romantics.

This was fused with the innate sexiness of his variations on the Little Black Dress.

The best look was a black kimono-style top, which billowed in great contrast to the tight, bright shiny black mini.

Subtle this was not, but then, subtle isn't glam-loving Vaccarello's thing.

VERONIQUE BRANQUINHO

It was the modern bohemian woman on parade.

Veronique Branquinho mixed and matched eclectic references, from wooden African bracelets to Obi-style dresses with belts.

The soundtrack included Marilyn Monroe's sultry "One Silver Dollar" from the Western "River of No Return," which played as cowboy boots and denim studs peppered the looks.

Stetson cowboy hats in Shetland went too far, but overall it was a strong collection for the up-and-coming designer reined in only by its feminine silhouette proportions and textural contrasts that unified the show.

The graceful, slouchy style, now a Branquinho signature, was seen on several of the dropped waist looks, often in beige and fawn.

LE MOINE TRICOTE

Fall-winter sees bright-eyed designer Alice Lemoine brimming with ideas.

First of all, in the unique presentation of her Le Moine Tricote collection via three different mediums in three different rooms: there were edgy photos, vintage-looking video projections, and the clothes themselves on mannequins.

Second of all, there were new ideas in the direction of the up-and-comer's knitwear line itself, which saw the repertoire this season spun out to include stricter woven fabrics. They provided a subtle but welcome contrast to the more feminine thick-knit tailored jackets in black, beige and gray.

The strongest piece in the show was a fantastic black mid-length coat dress that had pockets, a lapel and sleeves in billowing wool to imitate fur.

Despite sporty flashes, the collection overall remained thoroughly feminine, thanks to the natural roundness of the thick-knit silhouettes.

This season, ladylike is the name of the game.

CEDRIC CHARLIER

Architecture, "art brut" and Dutch Master Brueghel were all inspirations behind Cedric Charlier's diverse show.

The first pieces, among the collection's best, mixed up sharp geometric paneling alongside oversize coats with fluid, rounded shoulders.

Ensembles were made up of several layers, like square navy skirts on top of knee-length leggings with a rectangular bib form hanging down.

There were also some great structured sheaths in silky navy and black leather.

It's a far cry from the more fluid looks seen in Charlier's last collection.

The designer said medieval painter Brueghel inspired the bright colors of some of the prints and patterns, as did an early 20th century movement called "art brut" that celebrated art from shunned circles, like mental asylums.

It was an interesting idea that worked on the more simple silhouettes.

___

Thomas Adamson can be followed at http://Twitter.com/ThomasAdamsonAP

The online game maker's stock fell more than 10 percent in extended trading Wednesday after the first-quarter results came out.

Zynga, which makes "FarmVille" and other games, said Wednesday that it earned $4.1 million, which was breakeven per share. A year earlier, it lost $85.4 million, or 12 cents per share. Adjusted earnings were 1 cent per share in the latest quarter, compared with expectations for a loss of 3 cents.

Revenue fell 18 percent to $263.6 million, from $321 million.

Analysts, on average, had expected revenue of $264.5 million, according to FactSet.

As demand for its Facebook games fades, Zynga has cut jobs, closed game studios and shut down games to reduce expenses and focus only on popular titles. The quarter's expenses fell 34 percent to $268.5 million, from $406.6 million.

The number of people who play Zynga games at least once a month fell 13 percent to 253 million, from 292 million a year earlier. The number of daily players dropped 21 percent to 52 million, from 65 million.

CEO Mark Pincus said in a statement that 2013 will "continue to be a transition year." Zynga, whose games are played mainly on Facebook's website, is working on shifting to mobile games and to its own site off of Facebook.

For the current quarter, Zynga is forecasting an adjusted loss of 3 cents to 4 cents per share on revenue of $225 million to $235 million. Analysts were expecting a loss of 1 cent per share on revenue of $258.1 million.

Shares of San Francisco-based Zynga fell 34 cents, or 10.1 percent, to $3.01 in after-hours trading. The stock had closed up 17 cents, or 5.3 percent, at $3.35 before the results came out.

(Reuters) - Facebook Inc's mobile advertising revenue growth gained momentum in the first three months of the year as the social network sold more ads to users on smartphones and tablets, partially offsetting higher spending which weighed on profits.

New types of ads designed for smartphones, particularly ads aimed at enticing Facebook users to install mobile apps on their phones, helped lift revenue while traffic to the social network remained strong.

The results reassured Wall Street that the world's largest social network was keeping up with consumers' shift from PCs to smartphones, even if the company provided few big surprises during the first quarter.

Mobile ad revenue accounted for 30 percent of Facebook's ad revenue in the first quarter, compared to roughly 23 percent in the fourth quarter. Sales of ads on mobile devices have been a key element in the recovery of Facebook's overall ad revenue from a sharp slowdown early last year.

The first-quarter mobile ad revenue was at the higher end of expectations, said Macquarie Research analyst Ben Schachter. But he said it "needed to be higher for people to get really excited about trend lines".

Shares of Facebook, which are down roughly 12 percent since the end of January, were up 7 cents at $27.50 in after-hours trading on Wednesday.

"Everyone was focused on two things, one was mobile and how big it could be, and the other thing was engagement," said Ronald Josey, an analyst with JMP Securities.

Facebook delivered solid results on both fronts, Josey said, noting that consumers' use of Facebook does not appear to have declined despite a growing array of popular social networking and mobile messaging alternative services, such as Pinterest and WhatsApp.

Mark Zuckerberg, Facebook's 28-year-old co-founder and chief executive, told investors on a conference call on Wednesday that there was room for Facebook and rival services to thrive. He said mobile photo-sharing service Instagram, which Facebook acquired last year, was now growing faster than Facebook did at a similar stage in its history.

Facebook said it now counted 1.11 billion monthly active users and about 665 million daily active users.

The company said the number of monthly users who logged on solely through mobile devices more than doubled to 189 million users from a year ago.

Graphic: http://link.reuters.com/ryp77t

NEW AD PRODUCTS

Created in a Harvard dorm room in 2004, Facebook, along with other established Internet companies such as Google Inc and Yahoo Inc, are moving to reposition their businesses for a world in which consumers' primary Internet access occurs on small-screened smartphones rather than PCs.

Facebook has rolled out a string of big product launches and revamps in recent months, including an overhaul of its newsfeed and search feature, as well an app for Android smartphones that puts Facebook features front and center on phone homescreens.

The various initiatives have contributed to rising spending, with Facebook's 60 percent year-on-year increase in costs and expenses outpacing the 38 percent revenue increase.

Facebook said it earned $219 million, or 9 cents a share, in the first three months of the year, compared to $205 million, or 9 cents a share, in the year-ago period.

Excluding certain items, Facebook said it earned 12 cents a share. Analysts polled by Thomson Reuters I/B/E/S were looking for adjusted EPS of 13 cents.

Facebook executives reiterated previous guidance that spending would be up in 2013 as the company invests in new products and in improving the efficacy of its ads.

One nascent type of mobile advertising pioneered by Facebook ads that encourage users to install third-party apps could grow meaningfully, Zuckerberg said.

"We're starting to see real revenue from mobile app installs," Zuckerberg said, without giving details. "It's one of our most important new ad products."

Facebook's revenue in the first quarter totaled $1.46 billion, versus $1.06 billion in the year-ago period, and roughly in line with analyst expectations. Advertising revenue was up 43 percent in the first quarter, the fastest growth rate since the end of 2011.

"You are seeing pretty strong revenue growth right now," said Raymond James analyst Aaron Kessler. But he warned that the revenue growth could slow in coming quarters as Facebook faces tougher year-on-year comparisons.

(With additional reporting by Gerry Shih; Editing by Stephen Coates)

(This story was refiled to correct analyst Ronald Josey's firm to JMP Securities from Jefferies & Co in the seventh paragraph)

WASHINGTON/MIAMI (Reuters) - As detainees at the U.S. military prison in Guantanamo Bay, Cuba, press ahead with a widening hunger strike nearly three months old, President Barack Obama has come under increasing criticism for his policy of force-feeding them.

But U.S. law is on his side, an analysis of court rulings shows.

Most U.S. judges who have examined forced feeding in prisons have concluded that the measure may violate the rights of inmates to control their own bodies and to privacy - rights rooted in the U.S. Constitution and in common law. But they have found that the needs of operating a prison are more important.

Courts generally view a prison hunger strike as a suicide attempt, and they have ruled wardens have authority to stop suicide attempts as part of their mandate to preserve order.

"If prisoners were allowed to kill themselves, prisons would find it even more difficult than they do to maintain discipline, because of the effect of a suicide in agitating the other prisoners," Judge Richard Posner wrote for a Chicago-based appeals court in 2006 in a case involving a Wisconsin prison that punished a disobedient inmate by refusing him food.

As of Thursday, 94 of the 166 prisoners were on a hunger strike in Guantanamo, meaning they had refused at least nine consecutive meals. According to a military count, 17 had lost enough weight to be force-fed liquid meals through a nasogastric tube, and three were in the hospital for observation.

Army Lieutenant Colonel Samuel House, a spokesman for the detention camp, said none of the detainees in the hospital had a life-threatening condition.

Striking inmates began refusing to eat around early February, alleging rough handling of the Koran during searches for contraband and protesting their prolonged imprisonment. General John Kelly, head of U.S. military forces in Latin America, said assertions about the Koran were untrue.

OPPOSITION VOICED

A New York Times opinion piece last week by Samir Naji al Hasan Moqbel, a Yemeni man detained at Guantanamo since 2002, launched debate over the forced feedings. Like others there, he was captured abroad on suspicion of supporting terrorism.

"I will never forget the first time they passed the feeding tube up my nose. I can't describe how painful it is to be force-fed this way," Moqbel said in the op-ed dictated through an interpreter to his lawyers.

As described by Guantanamo officials, a feeding tube is lubricated and inserted through the nose down to the stomach for the two hours it takes liquid food to pass through. In general, hunger strikers continue to drink water.

Human rights advocates and many doctors decry forced feeding of hunger strikers as a violation of personal liberty and medical ethics with risks of medical complications such as discomfort, bleeding, nausea and throat sores. The 65-year-old World Medical Association, made up of 100 national medical associations, has said it is unethical and never justified to force-feed a mentally competent adult.

Carlos Warner, a federal public defender who represents 11 Guantanamo detainees, including Kuwaiti hunger striker Faiz al Kandari, said detainee lawyers are split on the issue.

Some "have a clear position that the government should not be force-feeding," and have unsuccessfully made their argument in federal court in Washington, D.C., Warner said. "Other lawyers are of the opinion that their clients should not die of hunger before we have a chance to free them."

The Constitution Project, a U.S. legal group that includes Democrats and Republicans, said last week that forced feeding at Guantanamo "is a form of abuse and must end."

George Annas, a Boston University professor of health law who opposes the forced feeding of hunger strikers on medical ethics grounds, said U.S. law is "very permissive" of the practice. He described the attitude of American prisons as: "Do we care about indignity? No, you're a prisoner, we'll treat you the way we want."

BARRIERS TO LEGAL CHALLENGE

The U.S. military argues forced feeding is not only legal but also humane. A federal judge agreed in 2009, ruling against Mohammed Bawazir, a Yemeni national held at Guantanamo since 2002. Bawazir called forced feeding torture.

Bawazir cited pain he experienced and use of a chair with "six-point restraints" that kept in place his forehead, limbs and torso. U.S. District Judge Gladys Kessler in Washington, D.C., said officials acted out of a need to preserve life.

A further barrier to any suit is the Military Commissions Act of 2006 which bars U.S. courts from hearing cases about Guantanamo detainee treatment. Even if they were to hear a challenge to forced feeding, the overriding evidence is the courts would rule against the detainees.

International law, which prohibits the inhuman or degrading treatment of prisoners, is not necessarily any help to Guantanamo detainees either.

The European Court of Human Rights has ruled at least twice that forced feeding amounted to torture, in a 2005 case out of Ukraine and in a 2007 case out of Moldova, but it stopped short of barring the procedure. The court said it may be used to preserve the life of hunger strikers if shown to be medically necessary and not done for punitive reasons.

Other reports of non-U.S. countries using forced feeding are rare, although experts said there is a lack of data. The practice has been described in news reports in Bahrain, China and Greece during the past decade.

Ten British-held Irish Republican Army prisoners, including former IRA commander Bobby Sands, starved to death in the Maze prison in Northern Ireland during a 1981 hunger strike during which they sought recognition as political prisoners. It ended when the families of the remaining hunger strikers authorized doctors to begin life-saving intravenous feeding as soon as the prisoners lost consciousness.

One early U.S. case involved Mark David Chapman, convicted in the 1980 killing of former Beatle John Lennon. Chapman broke a 26-day fast in 1982 only under a New York court-ordered threat he would be force-fed. Now 57, he is serving a prison sentence of 20 years to life.

Chapman had said he wanted to draw attention to starving children, but the court ruled the state's obligations to protect life and maintain order in its institutions outweighed Chapman's rights to free expression and to privacy.

BALANCING TEST

Most federal and state courts have agreed.

In Rhode Island, for example, finding that prisons have a duty to protect inmates' health, the State Supreme Court ruled in 1995 that "it would be in total disregard of this duty to stand idly by while a healthy adult decided to end his or her life by starvation just as it would if he or she decided to end his or her life by some more dramatic means such as hanging, slashing of wrists, or swallowing some type of poison."

Courts in three states - California, Florida and Georgia - have been exceptions, restricting forced feeding on various grounds, Mara Silver wrote in a 2005 Stanford Law Review article on the constitutional question of self-starvation.

California was the most sweeping. Prison officials must demonstrate "a threat to institutional security or public safety," not merely the conjecture of one, before denying an inmate the choice not to eat, the state's high court ruled.

Those are the exceptions however.

"The federal courts analyze the issue by balancing the prisoner's right to autonomy against the prison's right to maintain order, and they nearly always find that force-feeding is constitutional," said Margo Schlanger, a University of Michigan law professor with expertise in prisons.

(Editing by Howard Goller and Claudia Parsons)

No one was injured in the fire and firefighters and staff who rushed to the scene in central Copenhagen managed to save the majority of display items, museum spokesman Henrik Schilling said.

The fire started in the museum cafe around 2 a.m. and quickly spread to the exhibition hall. The last pockets of fire were being extinguished shortly after noon, Schilling said.

The museum is an affiliate of the Danish National Museum and exhibits objects related to the Danish resistance to the German occupation during World War II. The wooden building, located close to the waterfront, was built specifically for its purpose in the 1950s, Schilling said.

Nazi Germany's occupation of Denmark started on April 9, 1940, and continued until the Germans surrendered to the Allies on May 5, 1945. The Danish resistance movement distributed illegal flyers and upheld secret radio communication with the British. The resistance grew stronger toward the end of the war, when acts of violent sabotage against factories and railways increased.

The cause of the fire is not yet known. Schilling said it is still unclear if the building can be restored or needs to be rebuilt entirely.

RIO DE JANEIRO (Reuters) - Strong demand for mobile broadband equipment in Latin America will keep Ericsson's plant in Brazil at full capacity this year, says a senior executive at the telecom equipment manufacturer.

Mobile phone operators in Brazil are scrambling to improve their networks after heavy scrutiny from regulators because of poor service and a lack of investment in mobile infrastructure in recent years. The problems came despite a ballooning client base in Latin America's biggest economy.

But strong demand for faster, smartphone-friendly networks in neighboring countries is also fueling a growing need for mobile equipment elsewhere in the region.

"We see a growing demand in Latin America, both in 3G and 4G," said Andre Gildin, Ericsson's market intelligence director for the region, referring to the higher-speed networks that Brazil, Mexico, Colombia and other countries are rolling out.

The Swedish-based company expects 3G equipment to make up most of the demand this year in Brazil. Demand for 4G equipment is growing too as the industry begins building the country's fourth-generation mobile network.

The 4G effort is beginning in cities that in June will host soccer games during the Confederations Cup. The contest is a prelude to next year's World Cup, a much bigger event that is expected to strain Brazil's mobile telephone networks.

In 2012, about 40,000 pieces of mobile signal transmission equipment were produced at Ericsson's factory in the state of Sao Paulo. That took the factory to its production limit, a level that should be reached again by the end of the year.

"Our expectations are to finish this year with a similar number", Gildin said in an interview this week.

Half of this year's production will supply the Brazilian market, he added, while the rest would be exported to other Latin American countries. Big customers include operators in Mexico, which is implementing its 4G network, and Colombia, which is expanding both 4G and 3G services.

Argentina, Chile and Peru are also improving their mobile phone networks.

Ericsson says it has about 40 percent of the market in Brazil for 3G equipment. While the 3G network still has a long way to go in the country, the initial steps toward 4G services are helping the company get an early lead in that segment too, Gildin said.

Ericsson provides telecom gear, both 3G and 4G, to all four major Brazilian mobile operators - Telefonica's Vivo, Oi, Telecom Italia's TIM and America Movil's Claro.

Claro and Oi recently started to offer 4G services. Vivo and TIM are expect to announce their 4G plans next week.

Anatel, the Brazilian telecoms regulator, gave operators a deadline of next Tuesday to launch their 4G networks in the cities that will host the Confederations Cup.

(Editing by Paulo Prada and Peter Cooney)

ZTE is the latest in a line of hardware manufacturers that have struck a patent deal with Microsoft, which has successfully argued that Android - which Google provides free to handset makers - uses Microsoft-owned technology.

Google itself, and its Motorola phone maker unit, are the most notable holdouts against a patent agreement with Microsoft. Those differences could be settled soon, depending on the judge's verdict in a patent trial in Seattle.

Reaching agreement with ZTE means Microsoft now has patent deals in place with four of the five leading Android phone makers.

It already has agreements with South Korea's Samsung Electronics Co Ltd and LG Corp, and with Taiwan's HTC Corp.

It has no deal with China's fast-growing Huawei Technologies Co Ltd.

The ZTE deal marks progress for Microsoft with companies operating in China, following last week's patent agreement with contract manufacturer Hon Hai Precision Industry Co Ltd, parent of Foxconn.

Microsoft said it now has Android patent deals with about 20 device makers, and 60 percent of Android phones sold worldwide are covered by a Microsoft patent license.

(Reporting by Bill Rigby; Editing by Ryan Woo)

WASHINGTON (Reuters) - When a bipartisan group of senators began writing legislation to overhaul the nation's immigration laws in January, many Republican leaders embraced the effort as a savvy strategy for fixing the party's tattered image with Hispanic voters.

But since the bill was rolled out last week, a rift has emerged among conservatives that has played out in Senate hearings on Capitol Hill, on conservative talk shows and in social media such as Twitter and blogs.

The immigration effort has brought together an unusual coalition of Republicans, led by Florida Senator Marco Rubio, a potential 2016 presidential prospect, Arizona Senator John McCain, a former presidential candidate who has broken ranks with his party on some issues, and conservative anti-tax activist Grover Norquist.

But it has also put a spotlight on longstanding opposition to immigration reform within the party, potentially blunting the message party leaders had hoped to send in their efforts to remake the party's image, begun in earnest by the Republican National Committee after President Barack Obama swept to victory with 71 percent of the Hispanic vote in 2012.

Opponents of immigration reform include some traditional conservatives such as Senator Jeff Sessions of Alabama as well as some relative newcomers, including Texas Senator Ted Cruz, a Tea Party favorite. Another opponent of the immigration reform bill is Jim DeMint, a former South Carolina senator who is now president of the Heritage Foundation, a conservative think tank.

Luke Frans, executive director of Resurgent Republic, an organization that conducts polling and research for Republicans, said his group has met with Capitol Hill Republicans on the subject, advising them to avoid allowing the debate over immigration to become a "circular firing squad" in which Republicans are attacking their own.

"Conservatives have certainly seen in past debates where it's veered off the policy and become more of a personal tone. That's what we're really trying to avoid this time around," he said.

Critics of the legislation have labeled as "amnesty" a provision at the heart of the bill that would grant legal status to millions of undocumented immigrants. They also warn that the legislation would drive up the federal debt as immigrants eventually become eligible for federal benefits such as Social Security.

Supporters say providing legal status for the undocumented would bring people out of the shadows and ensure that they are working and paying taxes. Advocates also say the bill, which would establish new guest worker programs for both highly skilled and low-skilled workers, would boost the economy by making the labor market more flexible.

The debate is still in its early stages and many Republicans say the rancor is still far from the level that it reached in past immigration debates, such as one in 2006 and 2007 when criticism of comprehensive immigration reform on talk radio jammed phone lines at the Capitol.

But it may not be far beneath the surface either, to judge from some of the exchanges in the past week.

In a posting that highlighted the divisions among conservatives, Erick Erickson of the influential RedState political blog accused Rubio staffers and other supporters of the immigration bill of trying to paint critics as bigoted and racist.

Elsewhere, especially on Twitter, some conservative opponents of the immigration bill accused Rubio - falsely - of supporting the distribution of free phones to illegal immigrants.

Rubio has spent much of the last week appearing on conservative radio and TV stations to defend the legislation.

"We always realized that this was a complicated issue and that we were going to have to spend a lot of time explaining it," Rubio spokesman Alex Conant said. Conant described the response so far in conservative media as "mixed."

The bomb attack at the Boston Marathon last week that was allegedly carried out by two immigrant brothers of Chechnyan descent intensified the debate among Republicans over the immigration bill.

Some Republicans, including Senator Charles Grassley of Iowa and Senator Rand Paul of Kentucky, said the Boston attack, which killed three people and injured more than 250, were a reason to be cautious on immigration reform.

But other Republicans, including House of Representatives Speaker John Boehner and House Budget Committee Chairman Paul Ryan, argued that the Boston bombing showed the need to fix and modernize the immigration system.

While DeMint of the Heritage Foundation has been a vocal skeptic of the immigration reform bill, many of the scholars at two other influential conservative research organizations, the Cato Institute and the American Enterprise Institute, have been supportive of broad reform.

Charlie Black, a longtime adviser to Republican candidates who is now chairman of Prime Policy Group, a public affairs consulting firm, said the divisions among Republicans do not break down "along traditional lines" of conservative and moderate.

Whit Ayres, a Republican strategist who backs immigration reform, said Republican voters who may be skeptical of the effort are persuadable if proponents use the right message on immigration reform.

He said the strongest argument is that the current immigration system amounts to a "de facto amnesty" and that reforming the system is "better than anything (Democratic President) Barack Obama, left to his own devices, is likely to come up with."

Some conservative activists may be easier to persuade than others on immigration reform.

Chris Littleton of the Tea Party group Ohio Rising, said he did not understand what was behind all of the criticism of immigration reform.

"There are clearly employers who need low-cost labor and immigrants who want jobs, so there is clearly a functioning market here. Everybody's benefiting from the situation so I don't know why we need this debate," he said.

But David Crow of the Arkansas Conservative Caucus, another Tea Party group, said the proposed immigration bill would "simply create a magnet for more and more people to come across the border."

"In my opinion it is a huge mistake to go down this path when it's evident it will attract more and more illegal aliens," Crow added

(Additional reporting by Nick Carey; Editing by Fred Barbash and Lisa Shumaker)