PHILADELPHIA — Democrats Barack Obama and John Edwards sharply challenged Sen. Hillary Rodham Clinton’s candor, consistency and judgment Tuesday in a televised debate that underscored her front-runner status two months before the first presidential primary votes.

Obama, the Illinois senator, began immediately, saying Clinton has changed her positions on the North American Free Trade Agreement, torture policies and the Iraq war. Leadership, he said, does not mean “changing positions whenever it’s politically convenient.”

Edwards, the former North Carolina senator, was even sharper at times, saying Clinton “defends a broken system that’s corrupt in Washington, D.C.” He stood by his earlier claim that she has engaged in “doubletalk.”

Clinton, standing between the two men, largely shrugged off the remarks and defended her positions. She has been the focus of Republican candidates’ “conversations and consternation,” she said, because she is leading in the polls.

She said she has specific plans on Social Security, diplomacy and health care. “I have been standing against the Republicans, George Bush and Dick Cheney,” she said, “and I will continue to do so, and I think Democrats know that.”

Clinton defended her Senate vote in favor of designating Iran’s Revolutionary Guard as a terrorist group. Obama, Edwards and others have said Bush could interpret the measure as congressional approval for a military attack.

Edwards caustically challenged Clinton’s claim that she stands up to the Bush administration. “So the way to do that is to vote yes on a resolution that looks like it was written literally by the neocons?” he said.

“In my view, rushing to war — we should not be doing that — but we shouldn’t be doing nothing,” Clinton said. “And that means we should not let them acquire nuclear weapons, and the best way to prevent that is a full court press on the diplomatic front.”

Clinton also was the main focus during a discussion of the Iraq war. Again, Edwards leveled the toughest charges against the New York senator.

“If you believe that combat missions should be continued in Iraq” without a timetable for withdrawal, Edwards said, “then Senator Clinton is your candidate.” Edwards vowed to have all combat troops out of Iraq “in my first year in office.”

Clinton replied forcefully, saying “I stand for ending the war in Iraq, bringing our troops home.” She added, however, that “it is going to take time,” and some troops must remain to fight al-Qaida in Iraq.

“I don’t know how you pursue al-Qaida without engaging them in combat,” she said.

Edwards, drawing a link between Iraq and Iran, pressed on. “What I worry about is, if Bush invades Iran six months from now, I mean, are we going to hear: ‘If only I had known then what I know now?’ ” He was alluding to comments Clinton has made about her 2002 vote to authorize military action against Saddam Hussein.

Some candidates expressed frustration that most of the questions were directed to Clinton, Obama and Edwards. Seventeen minutes into the debate, Ohio Rep. Dennis Kucinich had yet to get a question and blurted out, “Is this a debate here?” Minutes later, New Mexico Gov. Bill Richardson threw up his hands in protest that he hadn’t been called on either and exchanged a frustrated glance with Kucinich.

It was the Democrats’ first debate in a month, and during that time Clinton has solidified her position as the front-runner, gaining in polls, taking the lead in fundraising and dominating the agenda.

Obama has criticized her for failing to explain how she would save Social Security and for a vote on Iran. Edwards has turned to questions of honesty and integrity, areas where polling shows voters are divided on Clinton.

The Clinton campaign on Tuesday posted videos of Obama and Edwards in the past saying they would campaign on hope, not tearing down their opponents, next to news reports of their criticisms of her.

Candidates participating in the debate were Clinton, Obama, Edwards, Delaware Sen. Joe Biden, Connecticut Sen. Chris Dodd, Richardson and Kucinich. Debate organizers excluded former Alaska Sen. Mike Gravel on grounds that he did not meet fundraising and polling thresholds.

Before the debate, the senators in the race said they would oppose Michael Mukasey’s confirmation as attorney general because he would not say that an interrogation technique called waterboarding amounts to torture.

Obama seized on a question noting that millions of pages of documents from the Clintons’ years in the White House are slowly being released by the National Archives. Moderator Tim Russert pressed Clinton on whether she would expedite their release and why her husband has suggested they remain private until 2012.

Obama, paraphrasing Sen. Clinton’s promise to turn the page on the Bush administration, said failing to release the Clinton papers is “an example of not turning the page.”

Richardson criticized his rivals for challenging Clinton so sharply, rebuking their “holier-than-thou attitude.”

Edwards and Dodd cited Clinton’s relatively high unfavorability ratings.

“Fifty percent won’t vote for her,” Dodd said.

On Social Security, Russert asked Clinton why she told an Iowa voter, in an offstage comment overheard by an Associated Press reporter, that she was open to raising the cap on payroll taxes when the proposal is not part of her platform.

Clinton said she did not have a “private position” on Social Security. She would convene a bipartisan commission to recommend ways to strengthen the program, she said, and all the well-known suggestions “would be considered.”

Only briefly did the candidates aim their remarks at Republicans. Delaware Sen. Joe Biden said former New York Mayor Rudy Giuliani “is genuinely not qualified to be president.”

Giuliani’s entire message is “a noun, a verb and 9/11,” Biden said, but that he had “done nothing” to implement anti-terrorism recommendations by the 9/11 Commission.