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Charles Dharapak, Associated Press
Republican presidential candidate, former Massachusetts Gov. Mitt Romney greets volunteers at his campaign office in Tampa, Fla., Tuesday, Jan. 31, 2012, during Florida's primary election day.

TAMPA, Fla. — Florida Republicans were putting an end to a raucous, big-spending, character-bashing primary campaign Tuesday as they decided whether a confident Mitt Romney or a defiant Newt Gingrich would win the state's 50 delegates, the biggest prize of the GOP race so far.

Romney grinned as he thanked campaign volunteers in Tampa, while Gingrich swooped in on polling places to shake voters' hands and complain that Romney had stymied him with outsized spending on "ads that are dishonest."

Romney, in turn, said he had been forced to defend himself on Florida's airwaves after losing to Gingrich in South Carolina — a loss he attributed to negative commercials aired on Gingrich's behalf.

"I needed to make sure that instead of being outgunned in terms of attacks, that I responded aggressively, and hopefully that will have served me well here," Romney told reporters.

Romney is heavily favored in the winner-takes-all primary, the final and possibly pivotal contest in a high-stakes month in which the former Massachusetts governor has claimed one win and two second-place finishes so far. Two other candidates — Rick Santorum and Ron Paul — have ceded Florida in favor of smaller, less expensive contests.

Gingrich dismissed suggestions that he might be hobbled by a significant loss in Florida, telling reporters outside an Orlando polling place that the race wouldn't be decided until June or July — "unless Romney drops out earlier."

Several Florida voters seemed eager for an end to the continuous volley of charges and countercharges that colored the campaign.

Dorothy Anderson, voting for Gingrich at a retirement community in Pinellas Park, Fla., said "The dirty ads really turned me off on Mitt Romney."

"In fact if he gets the nomination, I probably won't vote for him," Anderson added.

At the same polling place, Romney supporter Curtis Dempsey felt the same about voting for Gingrich if he becomes the nominee. Dempsey said "the only thing Newt Gingrich has to offer is a big mouth."

Romney and his allies have poured more than $14 million into Florida television advertising primarily attacking Gingrich, who has struggled to compete with Romney's fundraising ability, staffing and network of high-profile supporters. Gingrich and his allies spent roughly $3 million on Florida advertising, much of it attacking Romney.

In Miami's Little Havana, car salesman Osvaldo Mitat, 69, favored Gingrich. He's impressed by the former House speaker's "commitment to the Cuban community," Mitat said, and Gingrich's marital history doesn't bother him. Mitat has been divorced four times himself.

"Romney also has a past," he said. "Everyone has a past."

In Palm Beach, Julian Stoopler, a 68-year-old investment adviser, said he decided to vote for former business leader Romney. "The condition of the country has deteriorated so badly that we need a CEO to turn it around," Stoopler said.

For a time, Gingrich reset the GOP race with his overwhelming victory in South Carolina. But in the 10 days since, the contest turned increasingly hostile, Gingrich turned in uncharacteristically lackluster debate performances, and polls swung in Romney's direction.

Gingrich admitted that his momentum against Romney had slowed in Florida.

"He can bury me for a very short amount of time with four or five or six times as much money," Gingrich said in a television interview Monday. "In the long run, the Republican Party is not going to nominate ... a liberal Republican."

But, without predicting a winner or endorsing a candidate, Sen. Marco Rubio, R-Fla., told CNN: "The winner of Florida is in all likelihood going to be the nominee of our party."

The Gingrich campaign noted that he had raised more than $5 million in January, more than half following his win in South Carolina, after raising $10 million total in the last three months of 2011. Romney's campaign has said he pulled in more than twice that in the fourth quarter: $24 million.

Romney's campaign scheduled a night celebration at the Tampa Convention Center. Gingrich visited two polling stations and was stopping at the Polk County campaign headquarters before gathering with supporters for a primary night party in Orlando. The last polls close at 8 p.m.

The path to the Republican nomination — and the right to face President Barack Obama this fall — shifts to a series of lower-profile contests in February. Romney was to kick off the month Wednesday with events in Minnesota and Nevada.

The race for delegates is still in its early stages. A candidate needs to collect 1,144 delegates to win. Coming into Florida, Romney had 37 delegates to Gingrich's 26.

Santorum, who's won 14 delegates, and Paul, with four, chose to skip Florida on its primary day, instead campaigning across Colorado and Nevada. At Colorado State University, Paul spoke to a boisterous crowd of about 1,100, including Chase Swift, who shrugged off Paul's abdication of Florida. "Everyone thinks he has no chance," said Swift, 49, of Wellington. "Now we'll see."

Santorum bristled Tuesday when asked about Gingrich seeming to suggest that the former Pennsylvania senator should quit the race. "I don't think people should be telling other folks to get out of the race and get out of the way," Santorum told Fox News Channel.

Florida originally had 99 delegates but lost half as a penalty for holding its primary early, in violation of national party rules.

GOP officials in Florida were anticipating a big turnout of more than 2 million voters, up from a record 1.9 million in the Republican primary in 2008.

AP writers Christine Armario in Miami, Matt Sedensky in Palm Beach, Tamara Lush in Pinellas Park, Shannon McCaffrey in Orlando and Connie Cass in Washington contributed to this report.