Some U.S. officials are growing less confident that a major find will occur, a newspaper reports.
The Washington Post reports analysts are worried that their list of suspected sites might turn up empty.
After some of the best leads have tested negative, their hope of finding weapons increasingly rests on accidental finds — so troops are being sent to guard facilities like government ministries that weren't on the list of suspected sites.
The troops are to protect the facilities' contents from looters as well as regime agents trying to cover up their misdeeds or sell the weapons.
In arguing for war over the past months, the Bush administration contended not only that Iraq had weapons, but that it had massive quantities, including:
Thar means that finding an isolated set of warheads might not be a big enough "smoking gun."
If troops fail to uncover significant stockpiles, White House critics might conclude either that Iraq had no illegal arms, or that it has sold them off since the war. If the latter were true, the Post reports, the war will have spurred the very proliferation it was meant to stop.
U.S. officials are quick to point out that the search is still in its early days. The U.S. government is sending more than 1,000 experts specializing in weapons, intelligence and computers to join the hunt.
And officials tell the Post that the fact they are having trouble finding proof of Iraq's alleged illegal weapons does not mean the U.S. case for war was baseless.
"There's a common assumption that if you know they have chemical or biological weapons, then your intelligence should be good enough to know where they are," Under Secretary of Defense Douglas J. Feith told the newspaper. "But you may hear people talking, referring to specific substances or items, so you know from that that they have those substances or items" but not exactly where they are located.
In a possible breakthrough, U.S. military officials, speaking on condition of anonymity, confirmed they found material that could have been used to build chemical weapons.
However, many chemical weapons ingredients have nonmilitary purposes and officials cautioned that the findings, which are being analyzed, do not confirm the presence of chemical weapons.
The find was made several days ago with the help of an Iraqi scientist who claimed to have worked in Saddam's chemical weapons program.
The officials refused to name the scientist or identify the material, which had been buried in the ground.
According to the officials, who spoke on condition of anonymity, the scientist said the Iraqis set a warehouse on fire and destroyed chemical weapons and biological warfare equipment days before the war began March 20.
The scientist also said that several months before the war, he watched Iraqi officials bury chemical precursors for weapons and other sensitive material to conceal and protect them.
The Security Council was set to meet Tuesday to begin what is expected to be a tense debate over whether the inspection teams working in Iraq before the war should return.
The discussion is linked to Council consideration of Mr. Bush's request that sanctions against Iraq be lifted. Those sanctions are tied to Iraq's compliance with disarmament demands.
Russia wants the inspectors back in; the United States says it sees no role for them and has its own teams on the ground.
Chief U.N. weapons inspector Hans Blix says U.N. inspectors should return to Iraq to independently verify the discovery of any weapons of mass destruction.
In an interview with BBC radio aired Tuesday, Blix said before the war, the U.S. and Britain appeared to have used "shaky" intelligence, including forged documents, in an effort to prove Iraq had banned weapons.
Blix said it was "very, very disturbing" that U.S. intelligence failed to identify as fakes documents suggesting Iraq tried to buy uranium from the West African nation of Niger.
He also said U.S. officials tried to undermine his inspection team by telling the media that he withheld information about an Iraqi drone from the Security Council.