President Bush pledged again yesterday to rid Iraq of "weapons of terror," but coalition forces have so far failed to find proof of Iraqi biological or chemical weapons a week after the start of the U.S.-led invasion.

Pentagon officials pointed to the discovery Tuesday of Iraqi chemical protection suits at a hospital near Nasiriyah as evidence that Iraq's military had prepared for a chemical attack. Yet, the absence of Iraqi weapons of mass destruction -- either in the battlefield or in caches uncovered by U.S. troops -- has remained a notable feature of the military campaign so far, intelligence officials and weapons experts say.

Teams of weapons "hunters" acting on intelligence tips found no banned weapons yesterday during extensive searches of ammunition dumps near the port city of Umm Qasr. Earlier in the week, another team scoured a factory near Najaf that was initially thought to be a chemical-weapons plant. Numerous other sites identified as likely storage areas for biological or chemical weapons were searched by Special Forces units in the opening hours of the conflict, U.S. military officials have acknowledged. No unconventional weapons were found at any of the sites, the officials said.

The Bush administration has steadfastly maintained that such weapons would eventually be discovered. In his speech yesterday at McDill Air Force Base in Tampa, home of the U.S. Central Command, Bush sought again to frame the Iraqi campaign as a bid to "prevent the Iraqi regime from using its hidden weapons of mass destruction."

But in recent days U.S. officials have faced questions from reporters and open skepticism from other governments critical of U.S. policy toward Iraq. Secretary of State Colin L. Powell was confronted about the U.S. failure to find weapons in an interview with an Abu Dhabi television reporter. Powell said he was "quite confident" that Iraqi weapons of mass destruction would be found, but "right now we're trying to finish these battles, and that's our priority."

Tuesday's discovery of about 3,000 chemical protection suits and an assortment of gas masks and chemical antidotes at the Nasiriyah hospital appeared to bolster the administration's case, suggesting that Iraq was planning a chemical attack. Powell said the suits "must have been purchased because they thought chemical weapons might be present on the battlefield -- and the only ones who could deliver such chemical weapons would be the Iraqi armed forces."

But much about the discovered suits remained unclear yesterday, including how old they were and how the Iraqis intended to use them.

Weapons experts offered several explanations for the U.S. failure so far to find weapons. Some speculated that Saddam Hussein had decided to hold in reserve his most lethal weapons for use as a last resort and had entrusted them to elite units closest to him in the Iraqi capital. Others suggested the Iraqi president may have smuggled chemical and biological weapons out of the country for safe-keeping.

It is also possible that U.S. officials far overestimated Iraq's weapons holdings. While Iraq is known to have possessed significant numbers of chemical and biological weapons before the 1991 war, much of its arsenal was destroyed by allied bombings or U.N. weapons inspectors. The recent U.N. inspections that ended earlier this year found no evidence of biological or chemical weapons, but inspectors also could not substantiate Iraq's claims that it had destroyed its stockpile.

Joseph Cirincione, director of the Non-Proliferation Project of the Carnegie Endowment for International Peace, said the Bush administration had consistently emphasized the high end of U.N. estimates for the amount of weapons Hussein might still possess.

"It is equally possible that Iraq has very few biological or chemical weapons -- we just don't know," Cirincione said. "It could be that Saddam Hussein destroyed all or almost all of his munitions but left scientific teams and core assets intact so these programs could be quickly reconstituted later. In any case, the bar for President Bush is now very high: He has to deliver a large number of weapons to prove not only that Saddam Hussein was lying, but also that his weapons pose such an eminent threat that war is necessary."