CLEVELAND — Senator Clinton is getting a last, best chance tonight to slow Senator Obama’s momentum before the March 4 primaries in the last debate of an increasingly contentious Democratic presidential race.

Mr. Obama has won 11 straight primaries and caucuses, and even some of Mrs. Clinton’s supporters concede she must win in both Ohio and Texas next week to keep her candidacy alive.

“I think things have gotten a little hotter in the last couple of days,” Mr. Obama said at a news conference where he collected an endorsement from a former campaign rival, Senator Dodd of Connecticut.

There was unlikely to be any debate about that, after a four-day span in which Mrs. Clinton accused Mr. Obama of distorting her record on trade and health care in mass mailings, then criticized him as ill-prepared to take charge of the nation’s foreign policy.

Spicing the race further was a photograph of Mr. Obama that surfaced on the Internet, an image of him wearing a white turban and a wraparound white robe presented to him by elders in Wajir, in northeastern Kenya.

The gossip and news Web site The Drudge Report posted the photograph yesterday and said it was being circulated by “Clinton staffers.”

It offered no evidence of that, and Clinton aides said the campaign had not known the photo was being circulated and never sanctioned its distribution.

There were fresh signs of Mrs. Clinton’s campaign woes, including an AP-Ipsos poll that charted significant gains for Mr. Obama among male voters and others two months into the primary season.

In mid-January, Mrs. Clinton held a seven-point lead among all men, a group she now loses by 25 points. The two were about even among college graduates six weeks ago, and Mr. Obama now holds a 20-point margin.

The former first lady’s most reliable base of support continues to be older voters, women, and lower-income workers.

Mrs. Clinton campaigned in Lorain, a blue-collar city went of Cleveland several hours before the debate.

One man in the audience waved his arms and spoke emotionally about the legal struggles he has faced trying to hold onto his home.

“I can’t help everybody, but I try,” Mrs. Clinton said, after listening calmly. “There are a lot of people who really need help. We can’t treat each other like we are invisible.”

Mr. Obama’s only pre-debate public appearance was his news conference with Mr. Dodd, who said it was time for Democrats to unite for the fall campaign. He denied it was a nudge to Mrs. Clinton to quit the race.

In addition to Texas and Ohio, Rhode Island and Vermont hold primaries on March 4, with a total of 370 delegates at stake.