The remainder of the Democratic presidential contest may be a nasty one, judging by the sharp personal jabs senators Clinton and Obama traded last night during a sometimes-heated debate in South Carolina.

After Mrs. Clinton accused Mr. Obama of having expressed admiration for Republican ideas over the last decade or more, the Illinois senator said his record as a community organizer in Chicago during that time belied the notion that he would have affection for the agenda of people like President Reagan.

“While I was working on those streets, watching those folks see their jobs shift overseas, you were a corporate lawyer sitting on the board at Wal-Mart,” Mr. Obama said to the former first lady, who was a member of the Arkansas-based retailer’s board from 1986 to 1992. The Illinois senator denied complimenting Republican ideas and insisted when he talked of Republicans challenging conventional wisdom he was not endorsing those proposed innovations. “I didn’t say they were good ones,” he said.

“They were bad ideas,” Mrs. Clinton said, before suddenly unleashing a zinger over Mr. Obama’s ties to a Chicago developer who is under federal indictment for fraud, Antoin Rezko. “I was fighting against those ideas when you were practicing law and representing your contributor Rezko in his slum landlord business in inner-city Chicago,” she said.

Mr. Obama said the legal work Mrs. Clinton referred to was minimal and partly for a charitable group. “I was an associate at a law firm that represented a church group that had partnered with this individual to do a project and I did about five hours worth of work on this joint project,” he replied.

Mr. Obama did not address Mrs. Clinton’s description of Mr. Rezko as a slum owner, nor did the Illinois senator mention that he expanded his Chicago home by purchasing land from the developer in question.

A looming figure in the Democratic race, President Clinton, also provided fodder for the two hour debate, which was sponsored by CNN and the Congressional Black Caucus Institute. At one point, Mr. Obama complained that Mrs. Clinton had falsely asserted that the Illinois senator praised Reagan’s agenda. The former first lady said she never mentioned Reagan at all.

“Your husband did,” Mr. Obama said.

“Well, I’m here. He’s not,” Mrs. Clinton replied.

“I can’t tell who I’m running against sometimes,” the Illinois senator shot back.

The other candidate on stage in Myrtle Beach last night sometimes struggled to get a word in edgewise as the two leading candidates went at each other. “There is a third person in this debate,” Mr. Edwards complained at one juncture.

After one of the heated exchanges between Mr. Obama and Mrs. Clinton, the former senator from North Carolina tried to chide his opponents and rise above the fray. “This kind of squabbling—how many children is this going to get health care? How many people are going to get an education from this?” Mr. Edwards said.

Sometimes, however, Mr. Edwards jumped into the back and forth between the leading contenders. When Mrs. Clinton challenged Mr. Obama for voting against an amendment to impose a 30% maximum on annual credit card interest, he said, “I thought 30% was potentially too high of a ceiling.”

“So there’s no limit at all, Barack?” Mr. Edwards asked.

“You voted with the credit card companies. That’s the bottom line,” Mrs. Clinton responded. “You know, Senator Obama, it is very difficult having a straight-up debate with you, because you never take responsibility for any vote, and that has been a pattern,” she said.

Mrs. Clinton seemed satisfied with the retort, but the largely African-American audience in the debate hall erupted in sustained booing, seemingly suggesting that the New York senator had crossed some line.

Mr. Obama also came under attack over his health care proposal’s lack of a mandate that all individuals buy insurance if they don’t receive it from their employer or the government.

The Illinois senator said he wanted to focus on making insurance affordable before mandating it. He credited Mr. Edwards for being “honest” in saying some workers might have involuntary deductions from their paychecks to pay for insurance, but the Illinois senator said Mrs. Clinton “has not been clear about how that mandate will be enforced.”

Mrs. Clinton said Mr. Obama backed off support for a single-payer health plan, but the Illinois senator insisted he only suggested that such a plan would have been ideal if America did not have an existing system of employer-based insurance.

In e-mails to journalists, Mrs. Clinton’s campaign pointed out that not all of Mr. Obama’s endorsements of single-payer seem to have included that qualification.

One of the debate’s lighter moments came when Mr. Obama was asked whether he thought Mr. Clinton’s deserved his reputation as, in the words of Toni Morrison, “American first black president.”

“I would have to investigate more of Bill’s dancing abilities and some of this other stuff before I accurately judge whether he was in fact a brother,” Mr. Obama quipped.

Mrs. Clinton replied, “That can be arranged.”