Senator McCain of Arizona established himself as the front-runner for the Republican presidential nomination by defeating Mitt Romney in the Florida primary yesterday.

Mayor Giuliani, who campaigned intensely in the Sunshine State, saw his hopes dashed when he came in a distant third. The former mayor was poised last night to end his presidential bid, and reports said he was ready to throw his support behind Mr. McCain as soon as today.

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With 82% of precincts reporting, Mr. McCain had 643,204 votes, or 36%, Mr. Romney had 554,171 votes, or 31%, and Mr. Giuliani had 263,840 votes, or 15%. Michael Huckabee ran a close fourth, with 242,335 votes, or 14%.

Florida’s 57 Republican delegates are awarded on a winner-take-all basis, meaning that Mr. McCain will receive all of them even though he prevailed by only a few percentage points. It was Mr. McCain’s third primary win, after victories in New Hampshire and South Carolina. He had 93 delegates as of last night, compared with 59 for Mr. Romney.

“Our victory might not have reached landslide proportions, but it is sweet nonetheless,” a beaming Mr. McCain told supporters in Miami last night. He reached out to Mr. Romney’s backers, saying, “The margin that separated us tonight surely isn’t enough for me to brag about or for you to despair.”

Mr. McCain said he was confident he has gained the momentum to prevail in the 21-state Super Tuesday contest set for Tuesday. “In one week, we will have as close to a national primary as we’ve ever had in this country, I intend to win it and be the nominee of our party. … We have a ways to go, but we’re getting close.”

Mr. Romney did not dwell on the results, but he acknowledged that he had hoped to do better. “I’m sure that you are excited here this evening but a little disappointed as well,” he told a crowd in St. Petersburg, Fla.

The former Massachusetts governor said nothing about why his message seemed to have foundered in Florida. He quickly moved into his stump speech, which consists largely of veiled barbs at Mr. McCain. “Everybody looks to Washington for leadership, but Washington has failed us,” Mr. Romney said. “Washington is fundamentally broken and we’re not going to change Washington by sending the same people back just to sit in different chairs.”

Speaking to a sparsely attended gathering in Orlando, Mr. Giuliani referred to his presidential bid in the past tense, but did not confirm plans to endorse Mr. McCain today in California.

“I’m proud that we chose to stay positive and to run a campaign of ideas in an era of personal attacks, negative ads, and cynical spin. We ran a campaign that was uplifting,” Mr. Giuliani said. “You don’t always win, but you can always try to do it right.”

Mr. Giuliani sounded relaxed and a bit sentimental as he recognized senior campaign staffers and supporters one by one. He said he had no plans to retreat from public life. “We’ll stay involved,” he said. He outlined his platform in unusual detail, addressing national security, economic issues, tax cuts, school choice, and even tort reform.

However, the former mayor also alluded to some of the difficulties he faced in winning support from conservatives. “We’re a big party and we’re getting bigger. I’m even in this party,” he said with a laugh.

Mr. McCain seemed to be laying the groundwork last night for an endorsement from his rival, whom he called a “dear friend.” The Arizona senator said Mr. Giuliani “conducted himself with all the qualities of the exceptional American leader he truly is.”

County by county returns suggested that Mr. McCain, a former Navy pilot who was held as a prisoner of war in Vietnam, managed to stitch together a coalition of military families from Florida’s panhandle, moderates from Tampa and the South Florida suburbs, and a substantial number of Cuban-Americans from Miami, although many Cuban natives went for Mr. Giuliani.

Exit polls showed voters to be more concerned about the economy than the war in Iraq, immigration, or other issues. Mr. Romney, a former business consultant, was expected to benefit from the new focus on the economy, but the surveys said voters worried about the economy preferred Mr. McCain by a small margin. Mr. McCain won handily among self-described liberals and moderates, taking about 41%, and he held just about even with Mr. Romney among conservatives. Only those who said they were “very conservative” favored Mr. Romney, who got 44% of that group. Mr. McCain also scored some powerful last-minute endorsements in Florida, including Senator Martinez and Governor Charles Crist Jr. Mr. Romney had a financial advantage and blanketed the state in television advertising. The Florida results were expected to rejuvenate Mr. McCain’s fund-raising operation and to force Mr. Romney to decide whether to commit more of his own funds to a campaign facing increasingly long odds. He is estimated to have sunk $35 million into his bid thus far.

The map and the rules for the Super Tuesday contest seem to favor Mr. McCain. Many of the Northeastern states where he is likely to prevail are also winner-take-all. Many other states where Mr. Romney might fare better allocate voters proportionally, meaning Mr. McCain will pick up delegates even if he comes in second. Mr. Huckabee left Florida yesterday, heading for Creve Coeur, Mo., where he told supporters he was pleased with his showing in the latest contest, particularly in light of his campaign’s meager finances. “When you look at what we’ve done with what we have, it is a remarkable story that is not even close to being over. In fact, we’d like to believe were just really getting started,” the former Arkansas governor said.

Mr. Huckabee claimed a lead in most of the Southern states voting next week and said he would press on with his campaign, including the debate in California tonight. “I’m going to be on that stage,” he said. “I’m not sure everybody’s going to be there, but I will be.”