Rising U.S. Republican presidential contender Mike Huckabee will find himself in the cross hairs of rivals this week as the candidates face off in debates in Florida and Iowa.

Huckabee, a former governor of Arkansas, has vaulted past Mitt Romney to take the lead in many opinion polls in critical Iowa and taken over second place in other national polls behind Rudy Giuliani in the quest to be the party's candidate in the November presidential vote.

The Baptist preacher has soaked up support from Christian evangelicals in Iowa and in his native South, and he appears to be drawing interest away from the campaign of former Tennessee Sen. Fred Thompson.

At most recent debates, Huckabee has managed to stay above the fray while his rivals scrap with each other. But now his record in Arkansas might come under closer examination at one or both of the candidates' gatherings this week.

The new tone was evident on the Sunday talk show circuit where Huckabee faced the kind of grilling serious candidates receive when asked on "Fox News Sunday" about AIDS, immigration, religion and foreign policy issues.

The Romney camp accuses Huckabee of being a liberal and the Thompson campaign says Huckabee raised many taxes in Arkansas.

"He's going to get more scrutiny from the other candidates as well as from the press," said Andy Smith, a political scientist at the University of New Hampshire. "He's now a player."

For Romney, a Huckabee win in Iowa could be disastrous. A new Newsweek poll had Huckabee leading Romney by 39 percent to 17 percent among likely Republican caucus-goers in the state, where Romney was previously ahead.

Asked by a reporter while campaigning in South Carolina on Saturday whether he believed in polls, Huckabee said, "The good ones I do. All the good ones that have us ahead, I believe those. The other ones I don't."

Romney, a former Massachusetts governor, has spent millions of dollars and made multiple visits to Iowa, which on Jan. 3 begins the state-by-state battle to choose the Republican and Democratic candidates who will contest the November 2008 election for president.

Running way behind in national polls but leading in New Hampshire, Romney needs to win that state, which borders his home state of Massachusetts, and Iowa to generate momentum for the battles beyond.

"You might see him take on Huckabee directly," said Republican strategist Tony Fabrizio. "The key to him running the table is making sure Huckabee doesn't win Iowa."

ALL FACE BIG QUESTIONS

All of the leading Republicans face big questions in the muddled race for the party's presidential nomination.

Giuliani, while leading in national polls, has seen his advantage erode a bit and the former New York mayor has not been able to make much headway in New Hampshire, which holds a primary vote on Jan. 8.

Without much financial or organizational support, Huckabee has yet to prove he can carry his campaign past Iowa even if he deals a blow to Romney and he wins it. Fabrizio said a Huckabee victory in Iowa could help Giuliani improve his showing in New Hampshire.

Arizona Sen. John McCain is making noise in New Hampshire but needs to do well there to carry him forward.

McCain, speaking on "Fox News Sunday," said he detected "increased enthusiasm" in New Hampshire and repeated his prediction he would win the primary.

Illegal immigration and how U.S. policy might evolve toward Cuba with the declining health of leader Fidel Castro look to be leading topics at a Hispanic-oriented debate at the University of Miami on Sunday night.

The debate is being sponsored by Univision, the largest Spanish-language television network in the United States. The Republicans go at it again on Wednesday in Des Moines, Iowa.

Illegal immigration has been a difficult subject for Republicans since President George W. Bush's proposal to allow undocumented workers to get temporary work permits went down in flames in the Senate earlier this year.

The issue almost sank McCain's campaign -- conservatives rebelled against him for standing with Bush -- and the mantra in the party now is the need for stronger border enforcement.