WASHINGTON (AP) In the American hunt for Iraq's banned weapons, drums of suspicious chemicals turn out to be crop pesticide; a cache of white powder is found to be explosives.

More than six weeks into the Iraq campaign, there has been a string of false alarms but no discovery of what the Bush administration said was its main justification for going to war chemical, biological and nuclear weapons programs.

''As someone who supported the war, ... I wish they'd hurry up and find something,'' said John Pike, an analyst at GlobalSecurity.org.

But Defense Secretary Donald H. Rumsfeld says ''I'm not frustrated at all'' by the lack of evidence so far.

A military official involved with the search teams said last week they are under ''intense pressure from Washington to come up with something.'' The official, who spoke on condition of anonymity, said the teams are overwhelmed with work and looking forward to promised reinforcements.

''Clearly the administration has got to deliver the goods,'' said Charles Pena with the Washington-based Cato Institute.

And the United States will, President Bush and Cabinet officers insist.

''We'll find them, and it's just going to be a matter of time to do so,'' the president said Saturday.

''I'm absolutely sure that there are weapons of mass destruction there, and the evidence will be forthcoming,'' Secretary of State Colin Powell said Sunday.

But after scores of fruitless searches, other administration officials privately have stopped promising that. Some now say that instead of finding weapons stockpiles, they might find nothing more than documents and other evidence that the program once existed and was either destroyed or abandoned.

''Politically, this could be a big problem,'' said Paul Keer of the Arms Control Association, a Washington disarmament group. ''If it turns out they ... exaggerated, people will say we attacked without justification some are starting to say that now.''

Before the war, administration officials did not just say Iraq had weapons of mass destruction, they also said they knew where some of them were.

In an unsuccessful bid for U.N. approval for the war, Powell showed the Security Council satellite photos and intelligence he said indicated weapons were being moved, and he named sites where he said chemical weapons were held.

''The intelligence community still stands behind that information. I do,'' he said Sunday.

U.S.-led teams of military and civilian experts have reported finding nothing conclusive, however, after visiting most of some 100 sites that prewar American intelligence agencies said were the most probable hiding places. Hundreds more sites remain.

Expected intelligence from senior captured Iraqis who might have been most knowledgeable about the government's secrets is not materializing. One by one, they are insisting under interrogation that the government had no chemical, biological or nuclear weapons programs in recent years, U.S. officials say.

Pentagon officials said just days before the war that they had intelligence that chemical weapons had been distributed to some Iraqi military units. None has been found.

Hopes now may lie in greatly expanding the search effort. Advance teams for a group of some 1,000 experts, including former U.N. weapons inspectors and experts in intelligence, computers, demolition and such have started to arrive in the region to set up a larger program for analyzing intelligence, interrogating prisoners and scouring suspicious sites.

The new group will take control of the roughly 200 experts who have been searching so far, bringing additional expertise to the task. But officials say it is likely to be a couple of months before they are all assembled in Iraq.

Arguing for patience, Loren Thompson of the Washington-based Lexington Institute noted that U.N. inspections struggled with Iraq for a dozen years and could not find all they were looking for.

''I don't think the expectation was that this stuff would be sticking out like a sore thumb,'' he said. ''I think eventually they'll find the weapons, but the important point is that the government that would have thought to use them against us is gone.''

Some critics maintain that is not the point at all. They say the question always has been not whether Saddam had weapons, but whether those weapons were a big enough threat to the United States to justify war.

''If the Iraqis did not use them ... to defend an invasion of their own country, when were they ever going to use them, and how were they a threat to the United States?'' asked Cato Institute's Pena. ''That's the question that has to be asked and is being glossed over.''