WASHINGTON — As public opinion has swung increasingly against the war in Iraq, leading Democrats have seen little risk in demanding a withdrawal of American troops, buffeted by polls that show as many as seven in 10 voters are on their side.

What if the military situation in Iraq turns around?

That’s the question facing the party’s lawmakers and presidential candidates as Congress eagerly awaits a progress report next month from the American commander in Iraq, General David Petraeus.

Some political analysts say the Democrats have nothing to worry about. They argue the strength of public opinion against the war, combined with the inability of the Iraqi government to pass key legislation, have left the party on safe political turf in calling for an American exit.

Others are advising caution, warning that Democrats could lose the high ground if they are perceived to be ignoring evidence that President Bush’s troop “surge” is achieving success.

“The Republicans will exploit the hell out of that,” a Democratic political consultant, Daniel Gerstein, said.

The party, he said, now has a considerable advantage heading into 2008, due in large part to the war and to the unpopularity of the Bush administration. Mishandling the Petraeus report could put that in jeopardy, he said.

“If we don’t handle a shift in the facts on the ground in Iraq well, some of that advantage will erode, the Republican position will be strengthened, and we’ll have more of a jump ball, at least in the presidential election, than it’s shaping up to be right now,” Mr. Gerstein said.

Such concerns were underscored this week after the Democratic House whip, Rep. James Clyburn of South Carolina, told the Washington Post that a positive report from General Petraeus could split the party’s caucus and prove to be “a real big problem for us.”

In criticizing the administration, leading Democrats have generally tried to avoid language that Republicans could attack as overtly defeatist. As one Democrat who has recently turned against the war, Mayor Koch, put it: “Obviously, everyone who is interested in the country is going to be very happy” if America were to prevail.

The party’s top presidential candidates — Senator Clinton, Senator Obama of Illinois, and a former North Carolina senator, John Edwards — have all vociferously called for an end to the war, often trying to one-up each other on their anti-war credentials.

None have shown any indication that an encouraging outlook from General Petraeus would change their positions.

While unlikely, significant progress in Iraq would require a different line of thinking, a retired Air Force general who is advising Mr. Obama, Major General Scott Gration, said.

“Obviously if it’s very clear that the al-Maliki government is making significant progress, that we’re turning the tide, it would be crazy not to readjust,” General Gration said, adding that he was not speaking for the Obama campaign.

The Bush administration has said General Petraeus’s briefing next month should not be viewed as a decisive and final evaluation of the surge, and foreign policy analysts expect him to report some level of progress on the military front while saying it will take more time to fully secure key areas.

Supporters of the war have seized on a lower death toll among American troops in July, as well as an op-ed article in the New York Times by two policy analysts at the Brookings Institution who had previously criticized the administration’s strategy, Michael O’Hanlon and Kenneth Pollack. Reporting on their recent visit to Iraq, they wrote of significant military progress and high troop morale, advising Congress to stick with the surge into next year.

Some analysts predict that while Democrats may welcome achievements in security, they will zero in on political reconciliation efforts, where the news has been almost uniformly negative. “The military gains can’t last without political stability,” the president emeritus of the Council on Foreign Relations, Leslie Gelb, said.

To other political observers, American opposition to the war has hardened to a point where it is unlikely, if not impossible, to change. “The jury is in,” the editor of the Cook Political Report, Charles Cook, said. “I think the American people have made a decision on what they want to do in Iraq, and it’s not stay.”

The diminished credibility of the Bush administration in the eyes of many citizens also may temper any good news that General Petraeus delivers. “It better be believable,” a Democratic strategist, Robert Shrum, warned. “My guess is positions will not have changed.”

One analyst argued that anti-war sentiment is so strong that a positive report from General Petraeus would actually help Democrats in 2008, because by prolonging the war it would keep Iraq as the dominant political issue in the general election campaign. “Exactly what the Democrats want. They’ll never admit it,” the director of the University of Virginia’s Center for Politics, Larry Sabato, said. “It means that, one way or another, Bush can continue to fight his war until the last day of his administration, thereby nearly guaranteeing that the Democrats will win in 2008.”