REPORTS: IRAQI BASE HELD TOXIC GAS DURING BOMBING.

Byline: Philip Shenon The New York Times

U.S. intelligence reports show that the United States conducted an extensive bombing campaign during the Persian Gulf War against a sprawling ammunition depot in southern Iraq that was later determined to have then contained chemical weapons.

The Pentagon has previously acknowledged the possibility that some U.S. soldiers might have been exposed to Iraqi chemical or biological agents when U.S. combat engineers blew up part of the Kamisiyah ammunition depot in March 1991, after the Gulf War ended.

But the airstrikes raise the possibility that such agents wafted over thousands of U.S. troops in Saudi Arabia, where they were then preparing for the ground invasion of Iraq, several weeks before the engineers' operation.

Both the Pentagon and the United Nations, which is responsible for weapons inspections in Iraq, say they have no evidence that airstrikes on the depot resulted in the release of chemical weapons.

But many chemical agents dissipate quickly, which means there may have been no trace of them by the time inspectors arrived at the depot, months after the bombing.

Much of the rest of the depot was destroyed after the war by the engineers, many of whom have since complained of debilitating ailments that they link to exposure to chemical or biological agents there. Their symptoms, including chronic fatigue, digestive ailments and joint pain, are considered typical of the so-called Gulf War syndrome reported by thousands of U.S. soldiers.

The Pentagon announced in June, more than five years after the war, that it was investigating the possibility that the combat engineers might have been exposed to nerve gas when they blew up the complex.

And Pentagon officials said this week that as a result of those explosions, clouds of chemical agents may have wafted over more than 15,000 American troops, more than three times an earlier estimate.

A senior Pentagon official told reporters Wednesday that the belated appreciation of what occurred at Kamisiyah had caused the Defense Department to reconsider its entire approach to looking for evidence of Gulf War syndrome.

The official, speaking on condition of anonymity, said the events at Kamisiyah had made the Pentagon more vigilant in its examination of clues that might corroborate the claims of many veterans that they were made ill by chemicals during the war.

``Kamisiyah is a watershed in the search for information,'' he said. ``Kamisiyah is the first time we have been able to place American troops in the presence of chemical weapons. This changes the way we think about this subject.''

Among the several hundred engineers who helped demolish the Kamisiyah depot in 1991 and have recently been interviewed by the Pentagon, the official said, there has been no evidence of any extraordinary frequency of illness. But the official said the Pentagon was nonetheless establishing a special research team to review the Kamisiyah incident and to search for any similar incidents not yet discovered.