ORLANDO, Fla. — Mayor Giuliani told supporters today he’s abandoning his bid for president and backing Republican rival and longtime friend Senator McCain.

A New York Republican and adviser to Mr. Giuliani, Rep. Peter King, said the former mayor called him this morning to tell him of his plan.

Mr. Giuliani “will be announcing his endorsement today,” Mr. King said.

“I expect him to be fairly active for McCain. There is a real friendship and respect between the two,” he said. A similar call took place between Mr. Giuliani and New York Senate majority leader, Joseph Bruno.

“I spoke with Rudy Giuliani this morning and he confirmed that he is dropping out of the race and will endorse Senator John McCain for president,” Mr. Bruno said in a statement.

Once the Republican presidential front-runner, Mr. Giuliani suffered a debilitating defeat in yesterday’s Florida primary.

The former mayor finished a distant third to the winner, Mr. McCain, and close second-place finisher Mitt Romney. After the results, Republican officials had said Mr. Giuliani would endorse Mr. McCain today in California.

The officials spoke on condition of anonymity in advance of the public announcement.

Speaking to supporters last night, Mr. Giuliani stopped short of announcing he was stepping down, but delivered a valedictory speech that was more farewell than fight-on.

“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,” Mr. Giuliani said as supporters with tight smiles crowded behind him. “You don’t always win, but you can always try to do it right, and you did.”

Republican presidential candidates were scheduled to debate at the Reagan presidential library in Simi Valley on tonight.

“I haven’t talked to him,” Mr. McCain said as he boarded a campaign charter plane this morning. “I’m going to talk to him today when we meet.”