Tampa, Fla. ? 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 today. 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.