The national intelligence assessment on Iran’s nuclear program is forcing Senator Clinton to defend anew her vote to designate the Iranian Revolutionary Guard a terrorist organization, as her rivals for the Democratic presidential nomination seek to link her to what they call a “march to war” by the Bush administration.

Mrs. Clinton sparred with her opponents on Iran policy in an Iowa debate on National Public Radio yesterday afternoon, arguing that a nonbinding Senate resolution she supported in September had helped compel Tehran to back off its aid for American enemies in Iraq.

The former first lady was the only Democratic presidential candidate to support the measure, which also said the Iranian Revolutionary Guard were proliferating weapons of mass destruction. The national intelligence estimate declassified on Monday said Iran scuttled its nuclear weapons program in 2003.

Anticipating criticism from her leading competitors at the outset of the debate, Mrs. Clinton sought to drag Senator Obama of Illinois and John Edwards into her boat, citing hawkish statements they have made in recent years on Iran.

She said the Senate vote on designating the Revolutionary Guard as a terrorist group was part of a carrots-and-sticks diplomatic approach. Messrs. Obama and Edwards would have none of it. “Declaring a military group sponsored by the state of Iran a terrorist organization, that’s supposed to be diplomacy?” Mr. Edwards said dismissively. The former North Carolina senator said he and Mrs. Clinton had a “strong disagreement” on Iran and suggested that she was acquiescing to the Bush administration’s “saber-rattling” on Iran by voting for the resolution.

Mrs. Clinton appeared offended by the implication, launching into her most vigorous defense of the vote. “I understand politics, and I understand making outlandish political charges, but this really goes way too far,” she said. “In fact, having designated the Iranian Revolutionary Guard a terrorist organization, we’ve actually seen some changes in their behavior. There is absolutely no basis for a rush to war, which I oppose and have opposed for two years.”

Her argument drew a stern rebuke from Senator Biden of Delaware, who heads the Senate Foreign Relations Committee and opposed the Iran measure. “There’s no evidence — none, zero — that this declaration caused any change in action on the part of the Iranian government,” he said.

While there have been signs recently that Iran may have backed off its material and financial support for terrorists in Iraq, it is unclear whether the Senate action played any role.

President Bush yesterday downplayed the finding of the intelligence community that Iran had stopped its nuclear program four years ago, saying it had not changed his opinion that the regime in Tehran was dangerous and remained a potential threat to American security.

Even as she defended her Senate vote, Mrs. Clinton said yesterday she had the opposite reaction to this week’s report.

“I’m relieved that the intelligence community has reached this conclusion, but I vehemently disagree with the president that nothing’s changed and therefore nothing in American policy has to change,” she said.

The beginning exchange on Iran was by far the most combative in what was otherwise a polite and relatively substantive two-hour debate. The low-key tone after the opening minutes stood in contrast to the back-and-forth attacks emanating from the campaign trail in recent days, as Mrs. Clinton in particular has stepped up her criticism of Mr. Obama over his experience and record of leadership. Polls show an extremely tight race in Iowa, with Mrs. Clinton leading some surveys and Mr. Obama leading others.

NPR chose to focus the debate on three issues: Iran, China, and immigration. While the leading candidates aired differences on Iran, they broadly agreed on most issues dealing with America’s relationship with China and the question of immigration reform.

The top candidates all called for America to take a harder line on China’s human-rights violations, as well as in using current language in trade agreements to crack down on the importation of toys and other products contaminated with lead.

Asked if an individual should be responsible for turning over another person to authorities who they knew to be in America illegally, the hopefuls all said no.

“We do not deputize the American people to do the job that the federal government is supposed to do,” Mr. Obama said. He added: “I think that’s out of America’s character.”