"I know he's looking for some differences because you need them," he said to Edwards. "But there's not really a difference in this race between us in our commitment to get the lobbying out."
Edwards tried to play the aggressor -- albeit carefully -- throughout the debate, but Kerry, stung by the North Carolina senator's success in a Wisconsin debate less than two weeks ago, came armed to rebut his rival. In the Wisconsin debate, Edwards hurt Kerry by suggesting he had delivered a vague and evasive answer to a pointed question.
Thursday night, Kerry did the same to Edwards, who was asked repeatedly whether he regretted his vote for the Iraq war resolution.
"I believe I did what was right," Edwards said.
"Let me return a favor from the last debate," said Kerry, who also voted for the resolution. "You asked a yes-or-no question. . . . The answer is no."
The gay-marriage issue arose on a day when celebrity Rosie O'Donnell was married in San Francisco.
"What's happening here is this president is talking about first amending the United States Constitution for a problem that does not exist," Edwards said. "The law today does not require one state to recognize the marriage of another state."
Kerry was asked about his opposition to the 1996 Defense of Marriage Act, one of 14 senators to do so. He was reminded that he had opposed it in part because he believed it was unconstitutional and was asked whether Bush is correct in saying the only way to ensure that other states do not have to recognize gay marriages approved elsewhere is through a constitutional amendment. Kerry seemed to back away from his previous position.
"I think, under the 'full faith and credit' laws, that I was incorrect in that statement," Kerry said. "I think, in fact, that no state has to recognize something that is against their public policy. And for 200 years, we have left marriage up to the states. There is no showing whatsoever today that any state in the country, including my own -- which is now dealing with its own constitutional amendment -- is incapable of dealing with what they would like to do."
On the issue of Haiti, Kerry condemned the administration for its policy, saying that Bush officials have such dislike for President Jean-Bertrand Aristide that they have empowered the rebel forces not to negotiate in good faith. "He empowered them to veto any agreement."
Thursday's debate was the first of two among Kerry, Edwards, Rep. Dennis J. Kucinich (Ohio) and Al Sharpton before next week's Super Tuesday, when 10 states, including Maryland, will hold primaries or caucuses, with a total of 1,151 delegates, or almost 33 percent of the total for all the primaries, at stake.
The debate was also the first encounter since former Vermont governor Howard Dean ended his candidacy, and it offered Edwards an opportunity for what he said he has long wanted, the functional equivalent of a head-to-head debate with the front-runner.
In public polls, Kerry holds a substantial lead over Edwards in the two biggest states, California and New York, and is also ahead in two states Edwards has identified as his targets, Ohio and Georgia, although the margin in Georgia is in single digits.
Kucinich and Sharpton dealt with questions about why they remain in the race. Kucinich said he was there to present alternative views on health care and Iraq, where he favors ending the U.S. role.
Sharpton offered a series of one-liners but also had a retort to the independent candidacy of Ralph Nader. Nader, he said, should have joined the debate in the Democratic primaries, rather than standing outside. "He should have endorsed one of us," he said. "Let us come out with a winner and beat George Bush."
The debate was sponsored by CNN and the Los Angeles Times and was held on the campus of the University of Southern California.
Staff writer Paul Farhi contributed to this report.