President George W. Bush has increasingly justified the invasion of Iraq by saying US forces ended a brutal tyranny, even as he and top aides multiply suggestions the regime may have pre-emptively dismantled its arsenal.

"Perhaps over time we will find out what drove them to do that. Perhaps it was the fear of actually being discovered, caught red-handed with the very weapons we said they had," said White House spokesman Ari fleischer.

As clashes in Iraq become more sporadic, Bush may declare as early as next week that combat there has ended while stopping short of declaring victory because key missions remain, according to aides who requested anonymity.

Still, Bush remains confident that US-led forces scouring Iraq will find evidence of the weapons programs he placed at the core of his case for war, even though Baghdad always denied having them, said administration officials.

Another reason for caution is that Bush sees a global picture still rife with challenges -- like setting Iraq on course for democracy and winning the global war on terrorism -- which make declaring victory premature, they said.

And, observers said, Saddam Hussein's fate may not be known for certain by the time Bush speaks. The president recently announced that there was "some evidence" that the ousted leader was killed.

Bush's speech will look beyond the military triumph in Iraq to those other challenges, said the officials, who refused to say precisely when Bush would speak.

Fleischer said Friday that, "at the appropriate time," Bush will say "that the combat phase of the operation has come to a conclusion and that a new phase, the reconstruction of freedom, is beginning."

One possible venue for an address is the USS Abraham Lincoln, where Bush is scheduled to speak next Thursday before the aircraft carrier steams into port in southern California, said one aide.

The US leader has repeatedly said he will only declare the war is over when he hears that determination from the commander of US forces in the region, General Tommy Franks.

Such a message does not seem far off: The Pentagon declared April 14 that "major combat" was essentially over, and there have been few clashes of late involving US troops.

And Bush came close to saying things were wrapped up during a speech in Ohio on Thursday, declaring: "Now we have finished a war -- in the process of finishing a war in Iraq."

"The mission is not complete. Our forces still face danger in Iraq," added the president, who acknowledged that no conclusive evidence of Saddam's weapons has come to light since the invasion.

"But we know he had them, and whether he destroyed them, moved them or hid them, we're going to find out the truth," Bush said. "It's going to take time to find them."

In an interview with NBC television, he later said that interviews with captured Iraqis may yield damning evidence and said of Saddam: "Perhaps he destroyed some, perhaps he dispersed some."

"We have evidence now that we are gathering that shows that they may have destroyed some of them on the eve of the war -- they couldn't have destroyed them if they didn't have them," said Fleischer.