Democratic presidential front-runner Hillary Clinton fired back at her rivals and accused John Edwards of throwing mud on Thursday in a contentious debate marked by sharp clashes with Barack Obama and Edwards.

Clinton, who leads Democrats in national polls, went on the offensive early and delivered a strong performance in the first face-to-face encounter with her rivals since an October 30 debate where her candor and credibility came under fierce attack.

When somebody starts throwing mud at least we can hope it's accurate and not right out of the Republican playbook, Clinton said after Edwards questioned whether she could restore trust in the White House.

The debate featured harsh exchanges over Social Security, trade and foreign policy, with the tone reflecting the high stakes seven weeks before Iowa opens the state-by-state battle in each party to pick nominees for the November 2008 election.

Clinton was in the spotlight after a faltering performance in the last debate, when her campaign accused her rivals of piling on her. But Clinton's opponents did not back away, taking aim at her again.

She says she will bring change to Washington, while she continues to defend a system that does not work, that is broken, that is rigged and is corrupt, Edwards said.

Obama pointed again to her difficulty explaining whether she supported driver's licenses for illegal immigrants. She said on Wednesday she opposed the idea.

What the American people are looking for right now is straight answers to tough questions, and that is not what we've seen out of Senator Clinton on a host of issues, Obama said.

Obama also likened her to two top Republican presidential candidates for characterizing his plan to raise the income limits on Social Security taxes as a tax increase on the middle class.

This is the kind of thing that I would expect from Mitt Romney or Rudy Giuliani, where we start playing with numbers, Obama said.

The tone of the debate was criticized by New Mexico Gov. Bill Richardson and Delaware Sen. Joseph Biden, who slammed the continued Democratic assaults on each other.

'MUD-SLINGING'

Let's stop this mud-slinging, Richardson said.

Connecticut Sen. Chris Dodd said the shrillness in the Democratic presidential debates would hurt the party when it reached out to independents and Republicans in the general election.

When a campaign is about turning up the heat or who's angrier or who's yelling louder, the American people turn off, he said.

Edwards, a former senator from North Carolina, said there was nothing personal about his criticism of Clinton, a senator from New York who joked she was wearing an asbestos pantsuit to the debate at the University of Nevada-Las Vegas.

She said she was not playing the gender card with recent references to the all-boy's club of politics, and was not being attacked because she is a woman.

They are attacking me because I'm ahead, the former first lady said.

Clinton, who has proposed a health care plan that mandates universal coverage, took aim at Obama and Edwards for their health care records.

She said Edwards, who ran for president in 2004, did not support universal health care then, although he does now. She also criticized Obama's health care plan for leaving about 15 million Americans uncovered.

There is a big difference between Senator Obama and me. He starts from the premise of not reaching universal health care, she said.

Obama, an Illinois senator, said his plan also focused on bringing down costs.

I don't think the problem with the American people is that they are not being forced to get health care, the problem is they can't afford it, Obama said.

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