WASHINGTON — After a summer of mounting discontent over the war in Iraq, President Bush will face renewed criticism from Democrats and Republicans when Congress returns to work next week. But he appears unlikely to come up against an effective challenge to his policy, because his critics in both parties are deeply divided over what change in course to propose.

"There is an alternative strategy," said Sen. Joe Biden, D-Del., a foreign-policy critic of the administration, but "not a united one."

Over the past two months, as U.S. war casualties have risen and efforts to draft an Iraqi constitution have sputtered, public support for the war has sagged. War protesters, rallied by Cindy Sheehan, a California woman whose son died in Iraq, have dogged Bush at his ranch in Texas and at speeches in Idaho.

Some members of Congress have sharpened their criticism. Sen. Russ Feingold, D-Wis., who is considering a run for president, called on the administration to set a target of December 2006 for withdrawing all U.S. troops from Iraq.

Sen. Chuck Hagel, R-Neb., a maverick, said the war reminded him of Vietnam: "We're not winning," he said. "We should start figuring out how we get out of there."

Even Sen. Rick Santorum, R-Pa., a strong Bush ally in a tough race for re-election, said he had privately expressed "concerns" over the administration's management of the war. "I have a very clear track record of being supportive of the policy, but not necessarily all of the tactics," Santorum told The Philadelphia Inquirer.

But the most outspoken critics are, for now, lonely voices.

Few outspoken critics

Among Democrats, no senator has seconded Feingold's call for a withdrawal date. Among Republicans, none of Hagel's colleagues has endorsed his view of Iraq as a second Vietnam.

In the House of Representatives, a resolution calling on Bush to begin withdrawing troops by October 2006 gathered 45 co-sponsors by the midsummer congressional recess: 40 of the House's 202 Democrats, four of its 231 Republicans and one independent. Those numbers reflect a sharp contrast between the two parties in Congress.

A large majority of Republicans still support Bush's policy in Iraq, although some have been critical of the details. But Democrats appear increasingly divided between a small but growing caucus calling for withdrawal from Iraq, and a larger centrist group — including such potential presidential candidates as Biden and Sen. Hillary Rodham Clinton, D-N.Y. — that has stopped well short of that step.

"There's a base in the party that would give the president no power to go to war with Iraq," Biden said. But "the vast majority" of Democrats think otherwise, he said.

"This split has existed for some time. But the idea that the leaders of the party have stayed silent is just not accurate. I've made five major speeches, all of them saying we're running out of time."

Biden has called on the administration to increase the pace of training for Iraqi security forces, to seek more help from European countries and to enlist Syria, Saudi Arabia and Turkey — Iraq's neighbors — in what he calls "a regional policy" to stabilize the country.

He said he does not agree with calls for a specified withdrawal date for U.S. forces.

"Very different from Vietnam"

"This is very different from Vietnam," he said. "There's much more at stake." Nevertheless, he predicted: "By the end of '06 we'll be out of there — either because we've solidified the country, or it will be beyond our control."

The Democrats' divisions and the Republicans' relative unity also reflect what public-opinion polls have found: Opinion on Iraq appears polarized along partisan lines, with an increasing number of Democrats favoring a complete withdrawal of troops.

Most of the public may be "uneasy about the war," said White House counselor Dan Bartlett, Bush's top communications strategist, "but they don't support the precipitous withdrawal of troops."

And, he noted, when troop-withdrawal proposals have been made, "that debate is playing out more in the Democratic Party than in the Republican Party."

Bartlett said Bush has shown he is willing to debate Iraq policy and is convinced he is on strong ground.

"If you look at the criticisms," he added, "a lot of them are, 'Do it faster, do it better.' A lot of our critics are literally saying the same thing we are."

"There is obviously frustration out there; it has become an emotional issue," said another senior administration official who insisted on anonymity so he could speak more candidly. "The sentiment is: 'Do something!' But what are we going to do that we aren't already doing? Nobody has a good answer."

In an effort to shore up support for the war, Bush has launched a series of speeches defending his policy.

Administration officials say they think the antiwar protests led by Sheehan have largely misfired in the wider public, because Sheehan has criticized not only the war in Iraq but also the more popular war in Afghanistan. Those stances have allowed Bush and other officials to charge that their critics want the United States to withdraw from the entire Middle East, not just Iraq.

GOP pollster Whit Ayres said, public support for the war in Iraq depends largely on one factor: whether Americans believe progress is being made.

"Public opinion on Iraq is overwhelmingly driven by events on the ground," he said. "Events in Iraq matter far more than the number of American casualties or isolated protests. ... Americans don't like casualties, but they are willing to sustain casualties if they think it's worth it.

"If Iraq adopts and ratifies a constitution and elects a government, it will have a significant positive effect on public opinion and on people's willingness to sustain casualties and support the war," he said. "But if events on the ground devolve into less desirable conditions, popular support is likely to wane."

Los Angeles Times reporters Tyler Marshall and Peter Wallsten contributed to this report.