CLEVELAND — Senators Clinton and Obama blamed each other for spreading false information about their respective health care plans tonight in a high stakes debate one week before a quartet of primaries.

“Senator Obama has consistently said I would force people to have health care whether they can afford it or not,” Mrs. Clinton said, insisting it was not true.

Responding quickly, Mr. Obama countered that former first lady had consistently claimed his plan “would leave 15 million people out … I dispute that. I think it is inaccurate,” he said.

The tone was pointed yet polite in the early moments of the 90-minute encounter.

The two rivals, survivors of a grueling primary season, sat next to one another at a table on stage at Cleveland State University.

Mrs. Clinton also said as far as she knew her campaign had nothing to do with circulating a photograph of Mr. Obama 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, without substantiation, that it was being circulated by “Clinton staffers.”

“We have no evidence where it came from,” Mrs. Clinton said, making clear that’s not the kind of behavior she wants in her campaign.

“I take Senator Clinton at her word that she knew nothing about the photo,” Mr. Obama said.

In one curious moment, Mrs. Clinton said, “In the last several debates I seem to get the first question all the time. I don’t mind. I’ll be happy to field it. I just find it curious if anybody saw “Saturday Night Live,” maybe we should ask Barack if he’s comfortable and needs another pillow.”

In its episode last Saturday, the comedy show ran a feature portraying the news media as going easy on Mr. Obama, and a questioner asking at one point if he was comfortable and needed another pillow.

Mrs. Clinton angrily denounced Mr. Obama during the weekend for distorting her positions on health care and NAFTA and the debate moderator, Brian Williams of NBC News, showed a few seconds of her remarks.

Her comments at the debate table weren’t nearly as angry, but no less insistent.

“The charges that Senator Obama’s campaign has made regarding fliers and mailers and other information that he has been putting out about my health care plan and my position on NAFTA have been very disturbing to me,” she said.

When it was his turn to speak, Mr. Obama said Mrs. Clinton’s campaign has “constantly sent out negative attacks on us … We haven’t whined about it because I understand that’s the nature of these campaigns.”