Brian Blanco/European Pressphoto Agency

TAMPA — Mitt Romney raised the possibility that Newt Gingrich might have broken laws in representing corporate interests and warned of politically damaging “October surprises” if Mr. Gingrich became the Republican presidential nominee.

In Florida Reporting on the candidates and voters in the Sunshine State.

Speaking to reporters after a meeting with Florida residents who have lost their homes and businesses, Mr. Romney demanded that Mr. Gingrich release all documents related to his work for Freddie Mac, the mortgage giant, and other clients.

“Let’s see what they show; let’s see who his clients were,” Mr. Romney said, pointing specifically to work Mr. Gingrich did on behalf of health care companies. “That could represent not just evidence of lobbying, but potentially wrongful activity of some kind.”

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Mr. Romney did not elaborate about what illegal activity he suspected. And a spokesman for Mr. Romney declined to say whether Mr. Romney had specific knowledge about “wrongdoing” by Mr. Gingrich.

“We won’t know until they release records,” said Eric Fehrnstrom, a senior adviser for the campaign. “We’ll find out once he releases those documents. I don’t think we’ll know until he comes clean.”

Mr. Romney also demanded that Mr. Gingrich return the $1.7 million that he was paid by Freddie Mac, citing comments that Mr. Gingrich made during a debate last year that people who profited from the mortgage giant should give the money back.

And Mr. Romney repeated his concern that Mr. Gingrich had a record in public life that was “highly erratic.”

“He’s gone from pillar to post, almost like a pinball machine, from item to item, in a way which is highly erratic and does not suggest a stable, thoughtful course, which is normally associated with leadership,” Mr. Romney said.

The aggressive attacks on Mr. Gingrich come as Mr. Romney’s campaign sought to take the offensive after weeks in which he has been in a defensive crouch over his work at Bain Capital and his hesitance to release his personal tax returns.

Speaking on ABC’s “Good Morning America” before Mr. Romney’s remarks in Tampa, Mr. Gingrich insisted again that he had “done no lobbying work” for the mortgage institution and he accused Mr. Romney of lying.

“I did no lobbying, period,” Mr. Gingrich said. “It’s not true. He knows it’s not true. He is deliberately saying things he knows are false. I just think that’s what the next week will be like.”

But Mr. Gingrich called on the consulting organization he once led to release records about his work for Freddie Mac.

“I think it would be very helpful and our attorneys are talking with the company,” Mr. Gingrich said on ABC. “You know I left the company, so it’s their decision and Nancy Desmond, the president of the company, has to make the decision. But I’d be very comfortable releasing them.”

That is not likely to be good enough for Mr. Romney, who insisted that Mr. Gingrich was a lobbyist in spite of his denials.

“If it walks like a duck and quacks like a duck, it’s a duck,” Mr. Romney said. “We just need to understand what his activity has been over the last 15 years and make sure it’s conformed with all the regulations that might exist.”

Mr. Romney’s decision to focus on Mr. Gingrich’s work at Freddie Mac is also an attempt to tie Mr. Gingrich to the biggest economic crisis in Florida. On Monday morning, Mr. Romney convened a sober discussion about the housing crisis that is crushing this state.

The discussion with eight Florida residents who have lost their jobs and homes put human faces on those statistics, with several of the people around a small, round table telling Mr. Romney that they had lost their homes and businesses while they struggled to stay employed.

“I’m going to be living in my home until I get kicked out,” said Candice Tammey, a Tampa resident. “I’m able to pay my utilities. But it’s very discouraging. The system is not working for the people who really need it.”

Mr. Romney said at the discussion that nearly one quarter of all the homes in foreclosure in the country were in Florida. He called the situation for those around the table “tragic, tragic. Just tragic.”

“It will get better,” Mr. Romney promised Ms. Tammey. “It won’t always be like this. This is a detour.”

He added, “We’ve seen signs of improvement before only to drop back down” and said that if elected president, “I will care very deeply about getting it better very quickly.”

Mr. Romney’s campaign also said they planned to release its first negative television ad in Florida on Monday. The ad will say that Mr. Gingrich “cashed in” while Florida families suffered through the housing crisis, according to the campaign.

The campaign announced the ad during a conference call in which Tim Pawlenty, the former governor of Minnesota and a backer of Mr. Romney, repeatedly bashed Mr. Gingrich as an “influence peddler” in Washington.

“Newt Gingrich has spent almost his entire adult life as a member of Congress or someone who has been an influence peddler,” Mr. Pawlenty told reporters. “The notion that he was paid $1.7 million as a historian for Freddie Mac is just B.S. I mean it’s just nonsense.”

Mr. Pawlenty described Mr. Gingrich as someone who has “so many questionable and unfortunate activities.” And he demanded more transparency from Mr. Gingrich about his years after he left office.

“To say that he wasn’t a lobbyist is incredible hair splitting,” Mr. Pawlenty said.

Gingrich Responds

At a rally outside of Tampa, Mr. Gingrich responded to Mr. Romney’s attacks by repeatedly calling him a “desperate” candidate who will say anything to try and recover his footing.

“If you’ve been campaigning for six years and you begin to see it slip away, you get desperate,” Mr. Gingrich said of Mr. Romney. “And when you get desperate, you say almost anything.”

To the specifics of Mr. Romney’s attacks, Mr. Gingrich called them “baloney.”

“It used to be pious baloney, but now it’s desperate baloney,” Mr. Gingrich said, dismissing the accusations. “Pretty soon he’ll be able to open a delicatessen.”

Mr. Gingrich predicted that Mr. Romney would reprise his attacks at the debate Monday night, and he promised to be ready for whatever comes his way.

“I’ve been memorizing old phrases like ‘there you go again,'” Mr. Gingrich said, referring to a famous debate quip once used by Ronald Reagan. “I’m thinking maybe I’ll finally convince him I’m a Reaganite.”

Trip Gabriel contributed reporting.