By Michael D. Shear and Juliet Eilperin

SARASOTA, Fla., Jan. 26 -- Sen. John McCain of Arizona accused former Massachusetts governor Mitt Romney of having once supported a U.S. troop withdrawal from Iraq, sparking an angry demand for an apology from Romney, who called the statement "dishonest."

Both Republicans abandoned all pretense of civility as they campaigned across central Florida in advance of the state's primary Tuesday. Recent polls show a dead heat between McCain and Romney, and the winner here will gain a huge advantage as the nomination fight moves to 21 states a week later.

Stumping in Fort Myers on Saturday, McCain went on the attack first, linking Romney with Democratic Sen. Hillary Rodham Clinton (N.Y.): "If we surrender and wave a white flag, like Senator Clinton wants to do, and withdraw, as Governor Romney wanted to do, then there will be chaos, genocide, and the cost of American blood and treasure would be dramatically higher."

He added to reporters that "one of my opponents wanted to set a date for withdrawal that would have meant disaster."

Romney, who said in April that the military should consider a "private timetable" but not public deadlines, shot back: "That's dishonest, to say that I have a specific date. That's simply wrong. . . . I know he's trying desperately to change the topic from the economy and trying to get back to Iraq, but to say something that's not accurate is simply wrong, and he knows better."

Later, Romney added that McCain's comment on Iraq is "simply wrong and it's dishonest, and he should apologize."

The heightened tension between the two men represented a climax of sorts that has been building for months as they sparred for advantage in Iowa, New Hampshire, Michigan and South Carolina. While other candidates have been in that mix, the constant has been a battle between Romney and McCain -- two men who have not become friends on the trail.