GULF WAR ILLNESS-NERVE GAS LINK PROBED : U.S. SAYS BLAST AT IRAQ DEPOT RELEASED GASES.

Byline: Philip Shenon The New York Times

The Pentagon disclosed Friday that U.S. troops may have been exposed to nerve gas shortly after the war in the Persian Gulf when an Army unit blew up an Iraqi ammunition depot that contained rockets armed with chemical agents. The announcement may help explain some of the mysterious illnesses reported by U.S. troops who served in the gulf.

Defense Department officials said that when U.S. soldiers destroyed the depot in southern Iraq in March 1991, only days after the war ended, their monitoring equipment offered no indication that it contained chemical weapons. But the equipment may have been faulty.

And Pentagon officials said Friday that a visit to the site by United Nations investigators last month showed that there had been chemical agents in the depot - possibly mustard gas and sarin, a deadly nerve agent - and that they may have been released by the explosion.

``The new information here is that one of the exploded bunkers probably had chemical weapons inside it,'' said Kenneth Bacon, the Defense Department spokesman. ``Our understanding of this episode is still partial.''

The Pentagon has said consistently that there was no evidence that Iraq made use of its vast arsenal of chemical and biological weapons during the war, and Friday's announcement did nothing to undermine that assertion. Instead, the announcement seemed to suggest that if chemical agents were released, it was the work of U.S. troops, not the Iraqis.

The announcement could mark the beginnings of a dramatic policy reversal for the Pentagon, which has insisted in the past that it knew of no reason for the array of medical and psychological ailments reported by soldiers who served in the gulf.

More than 9,000 veterans have filed disability claims for ailments that they believe are related to the war, ranging from chronic fatigue to hair loss to memory loss, and collectively the ailments have become known as Gulf War Syndrome.

The Pentagon said Friday that 300 to 400 U.S. soldiers assigned to the Army's 37th Engineer Battalion were directly involved in the demolition of the Kamishiyah ammunition depot at Tal al-Lahm, in southern Iraq, between March 4 and March 7, 1991.

Dr. Stephen Joseph, the assistant secretary of defense for health affairs, said Friday that the Pentagon's initial review of its records showed ``no unusual frequency'' of illness among the soldiers who were closest to the explosion at the depot. ``There are no reports that we have located of acute illness in that time,'' he said at a news conference.

But Defense Department officials said they had begun a broad effort to crosscheck the roster of U.S. troops who were in that area of southern Iraq or downwind from the explosion against the list of 20,000 soldiers who have sought medical examinations for Gulf War Syndrome.

``We're positioned now to look at this area, look at our clinical data, look at what units were there at what time, and see if there are any matches,'' Joseph said at a news conference. ``What this does provide us is an area on which we must now focus our investigation.''

During the war, Czech chemical-weapons experts detected traces of nerve gas and a blister agent, leading Pentagon officials to theorize that the chemical agents may have been released as a result of a U.S. bombing attack on an Iraqi weapons plant. The officials said the amounts of chemical agent were so minute that they could not have posed a serious health threat to troops.

The Defense Department had no explanation Friday for how U.S. detection equipment deployed around the Kamishiyah depot could have been so faulty.

``The troops who destroyed that bunker were trained demolition experts, accompanied by chemical-weapons experts,'' Bacon said. ``They had inspected the bunker with chemical detectors prior to its destruction and found no evidence of chemical agents. Detectors in use during the destruction also did not confirm the presence of chemical agents.''

Asked how the Army's detection equipment could have failed to detect a large release of chemical agents, Bacon said, ``I can't speak to those theories now.'' He noted, however, ``We've done a lot in improving detection equipment since the Gulf War.''

As part of its cease-fire agreement with the United States and its allies, the Iraqi government acknowledged after the war that the Kamishiyah depot was one of several ammunition sites that had been used to store chemical weapons.

And the Defense Department acknowledged Friday that it received evidence in 1991 from U.N. weapons inspectors who had visited the site in October of that year and found trace amounts of sarin gas in the area.