As President Bush prepares to address the nation about Iraq tonight, a new Washington Post-ABC News poll finds that most Americans do not believe the administration's claims that impressive gains are being made against the insurgency, but a clear majority is willing to keep U.S. forces there for an extended time to stabilize the country.

The survey found that only one in eight Americans currently favors an immediate pullout of U.S. forces, while a solid majority continues to agree with Bush that the United States must remain in Iraq until civil order is restored -- a goal that most of those surveyed acknowledge is, at best, several years away.

Amid broad skepticism about Bush's credibility and whether the war was worth the cost, there were some encouraging signs for the president. A narrow majority -- 52 percent -- believes that the war has contributed to the long-term security of the United States, a five-point increase from earlier this month.

The findings crystallize the challenges facing Bush this evening in his nationally televised address from Fort Bragg, N.C., an event the administration sees as a critical opportunity for the president to restate the case for his Iraq policies. The goal is to reinvigorate public support for a war that has grown unpopular over time and convince Americans the administration has a policy that will lead to success over time.

So far, continuing spasms of violence in Iraq are competing with regular declarations of progress in Washington. Few people agree with Vice President Cheney's recent claim that the insurgency is in its "last throes." The survey found that 22 percent of Americans -- barely one in five -- say they believe that the insurgency is getting weaker, while 24 percent believe it is strengthening. More than half -- 53 percent -- say resistance to U.S. and Iraqi government forces has not changed, a view that matches the assessment offered last week in congressional testimony by the U.S. commander in Iraq, Gen. John P. Abizaid.

Views of the current status of the insurgency were deeply colored by partisanship. More than a third of all Republicans, 35 percent, agreed with the administration that the insurgents were growing weaker in Iraq, compared with 13 percent of all Democrats and 19 percent of all political independents.

By a narrow margin, the public continues to think the war has not been worth the cost and bigger majorities fear that Iraq has crippled the ability of the United States to respond to conflicts elsewhere in the world and has damaged efforts to recruit young people into the military. A large majority, about six in 10 people, say the United States is "bogged down" in Iraq.

Overwhelming majorities of Americans think the Bush administration and U.S. military leaders fundamentally underestimated the difficulty of the war and failed to anticipate the tenacity of the insurgency in Iraq.

Part of the administration's apparently growing credibility problem may be the result of recent disclosures about prewar planning, including what has come to be known as the Downing Street memo, reflecting notes of a July 2002 meeting with British Prime Minister Tony Blair and his top advisers. The memo said that the Bush administration had decided to go to war and that "the intelligence and facts were being fixed around the policy."

The administration has dismissed the conclusions of that memo, but the memo's wide circulation may have raised new doubts or reinforced old suspicions about Bush's motives for going to war. For the first time, a narrow majority -- 52 percent -- said the administration deliberately misled the public before the war, a nine-point increase in three months. Forty-eight percent said the administration told the public what it believed to be true at the time.

On a number of measures, public disapproval of Bush's policies has diminished slightly in the past month. Overall, however, Americans remain negative in most of their assessments about the cost of the war.

A majority -- 51 percent -- disapproves of the way Bush is handling his job as president, compared with 48 percent who approve, the same as a month ago. On Iraq, 56 percent disapprove of his handling of the situation vs. 43 percent who approve.

The survey found that opponents of Bush's policies feel more strongly about their views today than in the past, with four in 10 Americans saying they strongly disapprove of the job Bush is doing as president, the worst showing of his presidency. Just 27 percent strongly support him.

Despite public misgivings about elements of the policy, there remains an underlying reservoir of support for the war and continued unwillingness by the public to abandon Iraqis to their fate. Despite the almost daily suicide bombings and mounting casualty rates, a majority of Americans -- 53 percent -- now say they are optimistic about the situation in Iraq, up seven points from December.

The survey found the public sharply divided over another widely publicized administration claim. Speaking to an 80-nation conference on Iraq reconstruction in Brussels last week, Secretary of State Condoleezza Rice said that victory over anti-government forces will be "a death knell for terrorism as we know it" elsewhere.

Fewer than half -- 46 percent -- of those interviewed agreed that defeating the insurgents in Iraq would do much to defeat terrorism elsewhere, while 53 percent said it would have, at best, only limited impact on the broader anti-terrorism campaign. On that question, partisan divisions were striking. Seven in 10 Republicans agreed with the essence of Rice's statement, while an equal proportion of Democrats disagreed.

Throughout the survey, public dismay over the situation in Iraq alternated with more hopeful views. By a narrow margin, the public believes the United States is not making sufficient progress toward civil order in Iraq, and even more Americans, about six in 10, doubt that country will have a stable, democratic government a year from now. On the other hand, six in 10 say the elections in Iraq earlier this year brought it closer to the day that U.S. forces can be withdrawn. And overwhelming majorities believe the Iraqi people are better off now because of the war and will be better off in the future as a result of the U.S. invasion.

There were other findings suggesting that negative views of the conflict are easing somewhat. Currently, 51 percent believe that the war has contributed to the long-term stability of the Middle East, up nine points from a year ago. And the proportion who said the conflict damaged the United States' image with the rest of the world fell to 67 percent, down nine points since last June.

A total of 1,004 randomly selected adults were interviewed by telephone June 23-26 for this survey. The margin of sampling error for the overall results is plus or minus three percentage points.

Assistant polling director Claudia Deane contributed to this report.