MANCHESTER, N.H. — Under mounting pressure to shift the dynamic of the Democratic race, Sen. Hillary Rodham Clinton accused Sen. Barack Obama of being inconsistent on the issue of health care during a high-stakes debate among the top four contenders here Saturday night.

Obama calmly shot down Clinton's assertions that he scaled back his ambitions on health insurance in recent years, while former Sen. John Edwards rushed to align himself with Obama, delivering the harshest bromides of the night against Clinton as a symbol of entrenched Washington interests.

"Every time he speaks out for change," Edwards said of Obama, "every time I fight for change, the forces of status quo are going to attack, every single time."

As a pair of new polls showed the two front-runners even in New Hampshire, Clinton badly needed to blunt Obama's momentum after her disappointing third-place finish in the Iowa caucuses two nights earlier. Edwards hoped to propel himself into a one-on-one showdown with Obama after a second-place finish in Iowa, while Obama needed to exude confidence and avoid mistakes. New Mexico Gov. Bill Richardson was simply hoping to gain enough ground to hang on in the race.

Clinton charged Obama with inconsistency on health care and questioned his plan not to mandate that all Americans buy health insurance. Obama responded that there was a philosophical difference, saying he does not believe that a mandate is necessary because it is the cost of insurance that keeps people from buying insurance, not the lack of desire to do so.

But Clinton immediately challenged him by pointing out that his plan includes a mandate that parents buy insurance for their children. "Because they don't have a choice," Obama replied.

"Well, they don't have a choice, and you're going to make sure that parents get health care for children," Clinton said. "So, you know, you stopped short of going the distance to make sure that we had a system that could actually deliver health care for everyone."

When Clinton charged that Obama has not been specific about issues, he sought to turn the tables on her, saying he and Edwards have addressed the financial problems of Social Security by calling for raising the cap on wages covered by the payroll tax to force wealthy Americans to pay more.

"You criticized me for that, which is fine," he said. "We have a disagreement on that, but that's hardly because I wasn't specific on it. I was very specific on it."

The stage seemed to divide in half at moments, with Obama and Edwards, the first- and second-place winners of the Iowa caucuses, lining up against Clinton and Richardson, who defended the virtues of experience.

With the nomination on the line, Clinton explicitly mentioned gender as part of her appeal. "I think I am an agent of change. I embody change," she said. "I think having the first woman president is a huge change, with consequences across the country and the world." The audience at St. Anselm College erupted in cheers.

Clinton sharpened her case that she has been on the receiving end of so many special interest attacks that she knows how to fend them off, and at one moment, ABC moderator Charles Gibson even seemed to come to her defense, saying that in all his years of covering Washington, he has seen many candidates promise change.

Still, as she spoke of change, Clinton also turned to her husband's track record in the 1990s as part of her own. Referring to him as "President Clinton," she said his ability to tackle the budget deficit when he took office showed that candidates who promise change sometimes deliver it.

Richardson added: "Whatever happened to experience? Is experience a leper? We want to change this country. But you have to have, you have to know how to do it. And there's nothing wrong with having experience. So, I love change. We all are for change. But the question is, examine the record of those that in the past produced change."

Before the debate, Clinton rolled out a new campaign approach, dramatically shortening her stump speech and taking dozens of questions from voters in an effort to appear more at ease. Her campaign officials said the emphasis on questions and answers was designed to draw a contrast with Obama. They hoped that the more Clinton showed her command of the issues, the more it would force voters to question whether Obama has the same mastery of the issues and, ultimately, the readiness to be president.

Clinton's shift came as a CNN-WMUR poll taken by the University of New Hampshire showed Obama and Clinton tied at 33 percent, with Edwards at 20 percent. A week ago, Clinton led Obama, 34 percent to 30 percent. In a striking demographic development for Obama, he now runs evenly with Clinton among women for the first time (Clinton 33 percent, Obama 32); a week ago Clinton had an 11-point edge among women.