DOHA, Qatar - President Bush ended his whirlwind trip to Europe and the Middle East yesterday by flying over the battlefields of Iraq and promising American troops stationed in Qatar that the U.S. will find the weapons of mass destruction that were the key justification for toppling the regime of Saddam Hussein.

Speaking to 1,000 cheering troops at Camp As Sayliyah outside Doha, Bush dismissed criticism that the Iraqi threat was overstated. Hussein "spent decades hiding tools of mass murder," the president said. "He knew the inspectors were looking for them. You know better than me he's got a big country in which to hide them. We're on the look. We'll reveal the truth."

The White House and British Prime Minister Tony Blair, Bush's strongest wartime ally, have come under increasing pressure to turn up evidence of chemical, biological or nuclear weapons in Iraq. Critics have suggested that top officials in the U.S. and Britain misrepresented the intelligence reports on Hussein's capabilities to make his regime appear to be more of a threat than it was.

But in Qatar, Bush repeated his assertion that the United States has found evidence of weapons of mass destruction - in the form of two mobile facilities Bush said were capable of producing biological agents.

The mobile labs bore no trace of chemical weapons, but the Central Intelligence Agency and the Defense Intelligence Agency concluded in a report last month that they could not have had any "legitimate industrial use" and that production of biological weapons "is the only consistent, logical purpose for these vehicles."

Beyond the hunt for weapons, Bush said other discoveries since the war have proved the horrors of Hussein's regime.

"The world is now learning what many of you have seen," he told the soldiers. "They're learning about the mass graves, thousands of people just summarily executed. They're learning about the torture chambers. Because of you, a great evil has been ended. Because of you, the dignity of a great nation is being restored."

The speech amounted to a triumphal wrap-up of a trip that took Bush to a summit of industrial nations and a peacemaking stint in the Middle East, a journey designed in part to showcase the president's turning his attention from matters of war to peace and diplomacy.

Bush told the troops that the attacks of Sept. 11, 2001, and subsequent terrorist actions have awakened people around the world to the threat of such violence. "There is a universal recognition that the war on terror is just that - a war on terror, and not empty words," he said.

When Air Force One lifted off from Qatar, the president's plane flew over Iraq for about an hour on the way back to the United States. Bush sat on a bench and gazed out a left-side window of Air Force One along with Secretary of State Colin L. Powell, National Security Adviser Condoleezza Rice and White House chief of staff Andrew Card, according to White House spokesman Ari Fleischer.

Bush pointed out landmarks of the war, Fleischer said - including two airports, a predominantly Shiite area of Baghdad once known as Saddam City and a rural landscape where the war began with U.S. airstrikes on a "leadership site." Flying over Iraq instead of around it saved time on the homeward flight, but it also allowed Bush to "demonstrate that Iraq was free," a spokesman said. News reports said four F/A-18 fighter jets escorted Air Force One through Iraqi air space.

The centerpiece of the president's weeklong trip was a summit in Jordan with Israeli Prime Minster Ariel Sharon and new Palestinian Prime Minister Mahmoud Abbas. Both pledged concessions as they begin taking steps on a "road map" to peace, and Bush committed himself to a more active personal role in the peace process.

"He thinks it's a hopeful time," said a senior administration official aboard Air Force One yesterday. "The president had always said that when there was an opportunity to advance the peace process, he was prepared to do it and to do it with great vigor."

With the war in Iraq over and a new Palestinian prime minister who has renounced violence, "new conditions have begun to emerge that make this an opportunity that has more promise than we've had in quite a long time," the official said.

Others have noted that many previous peace initiatives by American presidents have fallen short, and that this one faces great obstacles as well.