Washington — As some of this city’s chattering classes had it, the Democratic presidential debate in New Hampshire Wednesday night was supposed to be a Hillary Clinton takedown. Senator Clinton had pulled so far ahead in the polls, the theory went, that her rivals would have to go negative to start to narrow the gap.

But on the stage at Dartmouth College, the attacks on Clinton were infrequent and mostly civil, despite repeated goading from moderator Tim Russert.

Hillary Clinton

“Not only did Tim Russert open the barn door,” says independent New Hampshire pollster Dick Bennett, “he tried to push the horse out and say, ‘Go for it.’ And they didn’t.”

Dante Scala, a University of New Hampshire political scientist, says that Clinton’s rivals appeared to decide that going negative too early could backfire – lowering their own poll numbers as much as they might Clinton’s.

Still, analysts say, the debate previewed what are likely to be intensifying lines of attacks as the primaries near.

“They’re building a negative argument gradually,” Mr. Scala says. “You don’t want to go too ballistic at this stage with-three-and a half months to go [to the primaries] — there’s a real danger to doing that too blatantly, especially in a multicandidate race.”

John Edwards delivered the sharpest challenge to Clinton Wednesday, suggesting that her Senate vote earlier in the day to label Iran’s Revolutionary Guard a terrorist group was paving the way for another misguided war.

Mr. Edwards said that he and Clinton “learned a very different lesson” from their 2002 votes to authorize the use of force in Iraq. The former North Carolina senator has apologized for his vote, while Clinton, though now a war critic, has not. “I have no intention,” Edwards said, “of giving George Bush the authority to take the first step on a road to war with Iran.”

Sen. Barack Obama, a distant second in the polls, took only one clear shot at Clinton, reacting belatedly to her remark that her failed healthcare initiative as first lady was a “lonely fight.”

“If it was lonely for Hillary,” Senator Obama said, “part of the reason it was lonely, Hillary, was because you closed the door to a lot of potential allies in that process.”

At another point, Obama seemed to allude to their differences over diplomacy with hostile nations. “One of the disagreements that we have on this stage is the degree to which the next president is going to have to engage in the sort of personal diplomacy that can bring about a new era [in the Middle East],” he said.

When Mr. Russert offered Sen. Chris Dodd a layup — asking about his recent statement that he could “understand why the president would want Senator Clinton to be the nominee” — Senator Dodd passed. “Being somewhat facetious,” Dodd said.

One of the night’s most pointed questions came from Russert, who asked how voters could trust Clinton’s leadership if two major actions — her 1993 health-care initiative and her vote for the Iraq war — turned out to be “fundamental misjudgments.”

Clinton acknowledged “mistakes” but quickly turned to her new health-care initiative, announced last week to generally favorable reviews. “I’ve come back with a different plan that I believe is much better reflective of what people want,” she said. “I want to be the healthcare president.” It was one of several tough questions Clinton deftly sidestepped.

The focus on Clinton comes as state and national polls show her with widening leads over her rivals for the Democratic nomination. In a CNN/WMUR poll this week of New Hampshire Democrats, 43 percent favored her, versus 20 percent for Obama and 12 percent for Edwards. In the same poll in July, Clinton led Obama 36 percent to 27 percent.

The poll found that growing numbers of New Hampshire Democrats see her as their best chance to defeat a Republican in the general election.

With Clinton’s lead, says Scala, “the struggle now is to define yourself as the challenger to the front-runner.”

Bennett, the pollster, gives the race for Democratic nomination one more month before the gloves come off. “At some point the candidates who aren’t leading are going to wake up in the middle of the night and say, ‘Ooh, I’m not going to win,'” he says. “When that morning comes, everything changes.”