Simi Valley, Calif. ? Newly-minted Republican presidential frontrunner John McCain and his chief rival Mitt Romney clashed Tuesday over Iraq and the economy, sometimes with tough talk, sometimes with dueling sets of facts, in the final GOP debate before 21 states around the country vote in GOP contests next week.

The last showdown featured McCain, fresh from a Florida primary victory and an afternoon endorsement by former New York Mayor Rudolph Giuliani, and Romney showing anger when they argued over whether Romney once endorsed timetables for ending U.S. involvement in Iraq.

McCain began this battle last Friday, when he cited a Romney quote from April. “Well,” the former Massachusetts governor had told ABC, “there’s no question that the president and Prime Minister al-Maliki have to have a series of timetables and milestones that they speak about, but those shouldn’t be for public pronouncement.”

Romney cried foul then and protested again Tuesday in the debate, held at the Ronald Reagan President Library.

“Unequivocally, absolutely no,” he insisted. “I have never ever supported a specific timetable for exit from Iraq, and it’s offensive to me that someone would suggest that I have.”

The “buzzword” among those who wanted withdrawal from Iraq, said McCain, was timetables, a word Romney had employed.

Romney protested how McCain raised the issue last weekend just before Florida’s crucial primary, “when there was very little time for me to correct the record … (it) sort of falls in the kind of dirty tricks that I think Ronald Reagan would have found to be reprehensible.”

McCain, who fixed a gentle smile on his face most of the night, looked tense. Romney, sitting to his left, usually answered with a half-smile and a determined look in his eye. The two men rarely looked at one another.

That was the night’s harshest exchange, but not the only one.

Romney charged McCain with too often being “outside the mainstream view of Republican thought.” McCain tried to brand Romney as a Massachusetts governor who imposed hundreds of millions of dollars of fees on constituents.

Another crucial issue that took on special poignancy in the Reagan library setting was which candidates are true Republican conservatives.

Romney, who fashioned himself a moderate during his Massachusetts career, painted himself Wednesday as a genuine GOP conservative; McCain countered by stressing his ability to “reach across the aisle” and work with Democrats.

Romney suggested that McCain indulges in bad bi-partisan habits. He offered a long list of instances where McCain broke from the party line: Restricting campaign finance and political speech; working with Independent Democrat Joe Lieberman on global warming initiatives, and cooperating with liberal icon Sen. Edward Kennedy to push immigration reform.

“Those views are outside the mainstream of conservative Republican thought,” Romney charged. “And I guess I’d also note that if you get endorsed by the New York Times you’re probably not a conservative.”

McCain, who got the Times’ nod recently, smiled.

“Let me note that I was endorsed by your two hometown newspapers, who know you best,” he said, “including the very conservative Boston Herald, who know you well, better than anybody.

“I’ll guarantee you the Arizona Republic will be endorsing me, my friend,” McCain, now almost laughing, said.

Former Arkansas Gov. Mike Huckabee and Texas Rep. Ron Paul, both far behind in most polls, also debated.