WASHINGTON – Facing sagging support for the war among Americans and in Congress, President Bush yesterday warned that if America leaves Iraq, “we will yield the future of the Middle East to men like bin Laden.”

In a rare reference to the Al Qaeda leader who plotted the attacks of September 11, 2001, Mr. Bush yesterday laid out why the fight was worth it in Iraq by quoting the Saudi terror master.

“Some wonder whether Iraq is a central front in the war on terror,” the president said. “Among the terrorists, there is no debate. Here are the words of Osama bin Laden: ‘This third world war is raging in Iraq. The whole world is watching this war.’ He says it will end in victory and glory or misery and humiliation.”

Toward the end of his speech, Mr. Bush vowed that America would “fight them there, we’ll fight them across the world, and we will stay in the fight until the fight is won.”

The president was speaking last night at Fort Bragg, the headquarters of the Army’s Special Forces, on the one-year anniversary of the coalition provisional authority’s handoff of governmental powers to an interim prime minister, Iyad Allawi. In 27 months of fighting, 1,740 American soldiers have been killed, and the official estimates of the cost of the war and reconstruction top $200 billion.

Not only have recent surveys suggested the president’s approval rating has dipped below 50%, but according to a recent Washington Post poll, less than 25% of Americans believe the insurgency is weakening, as Vice President Cheney suggested earlier this month.

Instead of claiming the terrorists were weakening, the president called attention to their venality. “We are fighting against men with blind hatred and armed with lethal weapons who are capable of any atrocity,” he said. “They wear no uniform, they respect no laws of warfare or morality. They take innocent lives to create chaos for the cameras. They are trying to shake our will in Iraq, just as they tried to shake our will on September 11, 2001.They will fail.”

Slumping support at home for the war has been coupled with a seemingly unrelenting tide of suicide attacks against Iraqi civilians and American soldiers. Yesterday, a second member of Iraq’s transitional national assembly was slain by insurgents.

In this context, many Democrats and some Republicans in Congress are calling for the troops to be withdrawn. Earlier this month, 123 Democrats and five Republicans in the House of Representatives voted for a resolution calling on a date for the military to exit Iraq.

Last week, Senator Hagel, a Republican of Nebraska, demanded that the White House level with the American people about the true state of affairs in Iraq. The Democratic grassroots group MoveOn.org, which implored its members to arrange parties to watch Michael Moore’s movie “Fahrenheit 9/11” during the 2004 campaign, featured Mr. Hagel’s words in a new advertisement calling for a withdrawal date. Mr. Hagel yesterday criticized the group for including his words in the commercial.

The president yesterday said the calls for withdrawal sent the wrong message to America’s soldiers, the Iraqi people, and the insurgency.

“Setting an artificial timetable would send the wrong message to the Iraqis, who need to know that America will not leave before the job is done,” the president said. “It would send the wrong signal to our troops, who need to know that we are serious about completing the mission they are risking their lives to achieve. And it would send the wrong message to the enemy, who would know that all they have to do is to wait us out.”

In answer to the question of when American soldiers could come home, the president said, “Our strategy can be summed up this way: As the Iraqis stand up, we will stand down.”

The president also made a plea for Americans to enlist in the military, a particularly poignant moment considering the Pentagon has failed to meet recruitment quotas in recent months. He also thanked the families of “good men and women who left our shores to defend freedom and did not live to make the journey home.”

“We pray for the families,” the president said. “And the best way to honor the lives that have been given in this struggle is to complete the mission.”

The president admitted yesterday that some of the Iraqi forces America was training were not quite ready for the battlefield. But he also said that new steps were being taken to embed American officers inside Iraqi units and to enable more Iraqi units to fight alongside coalition soldiers.

“Under U.S. command, they are providing battlefield advice and assistance to Iraqi forces during combat operations. Between battles, they are assisting the Iraqis with important skills such as urban combat and intelligence, surveillance and reconnaissance techniques,” the president said.

The Democrats yesterday did not offer up a prime-time speaker to address the American people after the president’s address. But on the floor of the Senate yesterday, Senator Kerry, the Massachusetts Democrat who lost the 2004 election to Mr. Bush, skewered the White House’s management of the war.

“While we shouldn’t dwell on mistakes, we need to understand their consequences on our ability to effectively move forward,” he said. “With … the American people realizing the rationalization for this war changed midstream, it becomes that much harder to rally the collective strength of the nation and the world to our cause.”

Senator Schumer echoed Mr. Kerry’s criticism after the president’s speech last night.

“It is not enough for the president to say ‘stay the course’ and make a few minor adjustments,” the New York Democrat said in a statement. “People want to know what the end game is, how the insurgency can be quelled, and when an Iraqi security force will be trained to take care of its own security needs.”