JACKSONVILLE, Fla. —  Mitt Romney and Newt Gingrich sparred over illegal immigration here Thursday night, with the former Massachusetts governor saying it was "repulsive" for the former House speaker to have characterized him as "the most anti-immigrant" candidate in the GOP presidential race.

The clash took place at the opening of the final debate before Tuesday's high-stakes Florida primary and reprised a long-running argument between the two leaders in the Republican contest. Earlier this week, Gingrich withdrew a political ad that had applied the "anti-immigrant" label to Romney, but when asked whether he believed that description was accurate, he said he did.

That brought rebuke from Romney.

"I'm not anti-immigrant," he said. "My father was born in Mexico. My wife's father was born in Wales. They came to this country. The idea that I'm anti-immigrant is repulsive. It's simply the kind of over-the-top rhetoric that has characterized American politics for too long."

Gingrich responded by noting that Romney earlier had harshly attacked him for suggesting that illegal immigrants who have been in the United States for a quarter-century or longer should be given the opportunity to become legal residents, though not citizens.

On Thursday, Romney conceded that he is not advocating rounding up such people.

"I'm not going to go find grandmothers and take them out of their home," he said.

The candidates then turned to Gingrich's work as a consultant for the housing agency Freddie Mac. The former speaker said again that his contract called for no lobbying, and then charged that Romney had significant investments in Freddie Mac and Fannie Mae.

Romney said his investments had been made through a blind trust and that in contrast, Ging rich had acted as a spokesman.

"What he was clearly doing was promoting ... Freddie Mac to the tune of $1.6 million," the former governor said.

Thursday's debate was the 19th of the season for the Republican candidates. Held at the University of North Florida, the forum was aired on CNN and moderated by the network's Wolf Blitzer. In addition to Romney and Gingrich, former Sen. Rick Santorum of Pennsylvania and Rep. Ron Paul of Texas participated.

The Florida primary will be a high-stakes battle that neither Gingrich nor Romney can afford to lose. Gingrich arrived riding the momentum from his victory Saturday in South Carolina, but polls here show a very close race. Gingrich, stung by the attacks from his opponent and a super PAC backing Romney, has lashed back with some of his angriest rhetoric of the campaign.

On Thursday morning, campaigning in Mount Dora, the former speaker accused Romney and the Republican establishment of slinging "mud" and "junk" because "they're against change in Washington."

Using the word "stupid" at least a dozen times to describe how Romney views voters, Gingrich said his rival's negative ads about Gingrich's consulting work for Freddie Mac are dishonest and hypocritical, and represent a desperate attempt by the establishment to block Gingrich's campaign.

"Well, I'm here as a citizen, and I frankly don't care what the Washington establishment thinks of me because I intend to change them," Gingrich said, prompting cheers and chants of "Newt! Newt! Newt!" from a crowd estimated at 1,500 people. "Remember: The Republican establishment is just as much as an establishment as the Democratic establishment, and they are just as determined to stop us."