Published: Jan 24, 2012 5:21 AM EST

STEVE PEOPLES/Associated Press

TAMPA, Fla. (AP) - Republican presidential contenders Mitt Romney and Newt Gingrich clashed repeatedly in heated, personal terms Monday night in a crackling campaign debate, the former Massachusetts governor tagging his rival as a Washington "influence peddler," only to be accused in turn of spreading falsehoods over many years in politics.

"You've been walking around the state saying things that are untrue," Gingrich told his rival in a two-hour debate marked by occasional interruptions and finger-pointing.

The event marked the first encounter among the four remaining GOP contenders - former Pennsylvania Sen. Rick Santorum and Texas Rep. Ron Paul shared the stage - since Gingrich won the South Carolina primary in an upset last weekend.

His double-digit victory reset the race to pick a rival to challenge Democratic President Barack Obama this fall, and the next contest is the Jan. 31 Florida primary.

With a week of campaigning ahead, Romney is expected to release his income tax return for 2010 as well as an estimate for 2011 on Tuesday. He said it will show he paid all the taxes he was obligated to pay, adding, "I don't think the voters want a president who pays more than he owes."

Following his defeat in South Carolina, Romney can ill afford to lose in Florida, and he was the aggressor from the opening moments Monday night. He said Gingrich had "resigned in disgrace" from Congress after four years as speaker and then had spent the next 15 years "working as an influence peddler."

In particular, he referred to the contract Gingrich's consulting firm had with Freddie Mac, a government-backed mortgage giant that he said "did a lot of bad for a lot of people and you were working there."

Romney also said Gingrich had lobbied lawmakers to approve legislation creating a new prescription drug benefit under Medicare.

"I have never, ever gone and done any lobbying," Gingrich retorted emphatically, adding that his firm had hired an expert to explain to employees "the bright line between what you can do as a citizen and what you do as a lobbyist."

Romney counterpunched, referring to the $300,000 that Gingrich's consulting firm received in 2006 from Freddie Mac, the government-backed mortgage giant.

And when Gingrich sought to turn the tables by inquiring about the private equity firm that Romney founded, the former Massachusetts governor replied: "We didn't do any work with the government. ...I wasn't a lobbyist."

As for the Medicare prescription drug benefit, Gingrich expressed pride in having supported it. "It has saved lives. It's run on a free enterprise model," he said in a state that is home to millions of seniors.

Whatever the stated subject, the debate's subtext was character - and electability, the quality that Republican voters say consistently matters most to them in the race.

Gingrich said voters don't want a president who will "manage the decay," but change the country. "That requires sending somebody who's prepared to be controversial when necessary."

Romney pointed to his career in business, his turn as head of the Salt Lake City Olympics and a term as governor of Massachusetts.

Obama took his lumps, as customary in a Republican debate.

Romney said the president lacks a vision for NASA, and said, "There are people on the Space Coast that are suffering and Florida itself is suffering as a result."

He proposed that "a collection" of academics and private investors consult with the president on a new mission for the space agency and have the program funded jointly by the government and private industry.

Gingrich called that answer "building a bigger bureaucracy" and instead proposed handing out prizes to people who come up with ways to "make the Space Coast literally hum with activity." Going back to the moon permanently, putting a man on mars and building space stations should be priorities, he said.

When the debate turned to immigration, one moderator noted that Romney and Santorum have said they would veto the "Dream Act," which would create conditions under which illegal immigrant minors might achieve U.S. citizenship, and asked if Gingrich agreed.

"No, I would work to get a signable version," he said. "I think any young person brought here by their parents when they were young should have the same opportunity to join the American military and earn citizenship."

Romney said that was the same as his position.

Moments later, he was asked to reconcile two other statements he has made about immigration, that while he doesn't want to deport millions of illegal immigrants, he wants them to return to their home countries and apply for citizenship. "The answer is self-deportation, which is people decide they can do better by going home," he said.

At times, the other two contenders on stage were reduced to supporting roles.

Asked if he could envision a path to the nomination for himself, Santorum said the race has so far been defined by its unpredictability.

He jumped at the chance to criticize both Romney and Gingrich for having supported the big federal bailouts of Wall Street in 2008.

He also said both men had abandoned conservative principles by supporting elements of "cap and trade" legislation to curb pollution emissions from industrial sites. "When push came to shove, they were pushed," he said.

Paul sidestepped when moderator Brian Williams of NBC asked if he would run as a third-party candidate in the fall if he doesn't win the nomination. "I have no intention," he said, but he didn't rule it out.

Paul has said he will largely bypass Florida to concentrate on states that are holding caucuses.

Hit at the outset with Romney' charge that he had resigned Congress in disgrace and went on to a career peddling his own influence, Gingrich said two men who had run against the former governor in the 2008 campaign, John McCain and Mike Huckabee, had said he couldn't tell the truth.

The polls post-South Carolina show Gingrich and Romney leading in the Florida primary. That and the former speaker's weekend victory explained why the two were squabbling even before the debate began, and why they tangled almost instantly once it had begun.

Romney began airing a harshly critical new campaign ad and said the former House speaker had engaged in "potentially wrongful activity" with the consulting work he did after leaving Congress in the late 1990s.

Gingrich retorted that Romney was a candidate who was campaigning on openness yet "has released none of his business records."

He followed up two hours before the debate by arranging the release of a contract his former consulting firm had with the Federal Home Loan Mortgage Corp. for a retainer of $25,000 per month in 2006, or a total for the year of $300,000. The agreement called for "consulting and related services."

Despite Romney's attempts to call Gingrich a lobbyist, the contract makes no mention of lobbying.

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