ST. PETERSBURG, Fla. — Governor Crist of Florida endorsed a beaming Senator McCain last night, delivering a boost three days before the state’s pivotal primary.

Mr. Crist praised Mr. McCain as a “true American hero.” At a county Republican dinner in St. Petersburg, Mr. Crist added, “After thinking about it as much as I have, I don’t think anybody would do better than the man who stands next to me, Senator John McCain.”

It was the second high-profile endorsement in as many days for Mr. McCain, who is locked in a tight primary race with a former Massachusetts governor, Mitt Romney. Mr. Crist stepped to the podium a little more than 24 hours after Senator Martinez announced he was backing his colleague in the Senate. Officials said Mr. Martinez, who campaigned yesterday with Mr. McCain, had prodded the governor to follow his lead.

Mr. Crist said he would campaign for Mr. McCain in the coming days. “I just feel in my heart he’s the right man for the job at the right time,” he told reporters afterward.

The winner of next week’s primary will capture all 57 delegates at stake, a large prize that will set the stage for a virtual nationwide primary on February 5.

Mr. Crist’s endorsement was sought by all the Republican presidential rivals, including Mr. Romney, Mayor Giuliani and a former Arkansas governor, Michael Huckabee.

Mr. McCain said the nod “means a lot in this race.”

“I’m honored and privileged,” Mr. McCain told reporters. “And I intend to work very closely with him on the issues. We’ve got to provide home insurance for every person who lives in the path of a hurricane. We are going to have to work together to save the Everglades and other great environmental treasures of this state.”

He quipped: “We will continue to compete for both baseball spring training and for tourism.”