In a contentious debate, the third man on the stage, Alan Keyes, chided the top contenders for their "pointless squabbling."

Squabbling, yes. Pointless, no. McCain and Bush are making strategic strikes, knowing the consequences will be severe if they go too soft or too hard.

McCain seemed to find the balance he sought, defending himself against criticism while striking out at Bush with a smile on his face. He used a stiletto, not a sledgehammer, to dispute the Texas governor's portrayal of his tax policies.

"It's not a Washington mentality, it's the grownup mentality," McCain said, suggesting that Bush is not mature enough to be president.

Bush, combative on the heels of his landslide defeat in New Hampshire, spoke with exclamation-point passion.

"You don't know my record!" he told Keyes.

"Let me finish! Let me finish!" he told McCain.

"We need to be a pro-life party!" he told moderator Larry King.

The Texas governor, pulling out a McCain campaign flyer that criticized Bush's tax-cutting plan, accused the Arizona senator of breaking his pledge to run a positive campaign.

"That is not by my campaign," McCain said, pointing to the paper.

"It says, `Paid for by John McCain," Bush fired back. Indeed, McCain acknowledged later that the handout was produced by his campaign, but said his staff had nothing to do with handing it out.

Supporters who had urged Bush to be more aggressive had to be happy with his performance.

"Ever since New Hampshire, it has been important for him to show he's willing to fight for the nomination," said GOP consultant Scott Reed, who is not tied to any of the campaigns. "I thought his fire was healthy, actually."

The debate was the candidates' final shot at a wide audience before Saturday's primary, a flash point in the intense nomination fight. Contests in Michigan and McCain's home state of Arizona are one week away, little time for a loser here to regain his footing.

"A lot of people will decide who to vote for, and just as important whether or not to vote, based on the debate," said Dave Woodard, a GOP consultant and professor at Clemson University.

McCain used a lengthy discussion of foreign policy to draw a subtle distinction with Bush.

When the Texas governor said the United States must be careful where it deploys forces, McCain seemed dismissive. "It's not that simple," he said, then argued that a superpower must keep its options open.

While McCain provided crisp, clear answers to foreign policy questions, Bush sometimes rambled. "I don't know. I don't know. Probably not. Maybe," Bush said when asked if he would meet with Russian President Vladimir Putin as the Republican nominee.

"McCain really came through on the foreign policy and national defense issues as somebody who looks presidential," Reed said. He said Bush produced "a lot of unforced errors."

McCain hopes to return to the form that helped him win New Hampshire's primary. He let Bush get under his skin in the opening days of the South Carolina race and approved a highly critical ad -- what one chagrined adviser now calls "an electronic temper-tantrum."

It suggested that Bush, like President Clinton, couldn't be trusted. A follow- up ad found Bush guilty of "truth twisting." McCain had been set off by an ad that said he wasn't telling the truth about Bush, but that one didn't make the comparison to Clinton -- the ultimate insult in GOP politics.

After his own polling suggested the spots had backfired, McCain yanked them and promised to run a clean campaign. The ads had tarnished his image and threatened to suppress voter turnout; McCain needs a large showing of new GOP primary voters.

Bush needed to undermine McCain's credibility to slow his momentum, but the strategy was risky. Voters may be turned off by his rhetoric or the work of his surrogates.

"They're both in a box," Woodard said. "The perception has been that both have honor, courage and dignity -- the things people are looking for in the wake of the Monica Lewinsky scandal. And when you go negative, you look like President Clinton."

McCain, even more than Bush, suffers if voters feel a debate is too negative; he is the only candidate promising to defeat the establishment and change the way campaigns are run.

"People could begin saying, `This is politics as usual, not politics that's different," Woodard said.