A federal watchdog agency says that at a time when U.S. Air Force pilots and aircrews are at a premium for potential wartime duty in Iraq, a substantial number have either left the military, transferred to non-flying duties or moved to inactive status to avoid the controversial anthrax vaccine.

The U.S. General Accounting Office said about 16 percent of National Guard and Reserve pilots and aircrew members changed their status between September 1998 and September 2000. Another 18 percent of those still assigned to or participating in a flying unit in 2000, said they wanted to leave soon, the agency said.

The vaccine is being given first to service members assigned to high-risk areas, and pilots are typically at the top of that list.

Both groups - those who had left and those planning to leave - ranked the mandatory anthrax vaccination program as the "key factor" in their decisions.

Reginald J. Brown, Assistant Secretary of the Army, said the pilot and aircrew resignation and military separation figures in the GAO survey are consistent with the figures from before the mandatory vaccination program began.

The GAO estimated that 24 percent of those who left the military did so before qualifying for military retirement benefits. And it said those changing status or planning to do so had accumulated an average of 3,000 flight hours, "representing the loss of a very seasoned workforce," the report says.

The GAO estimated that, on average, a pilot with nine years of experience cost the government about $6 million to train.

At the time of the survey in September 2000, the GAO said 37 percent of the Guard and reserve pilots and aircrew said they had received one or more anthrax shots, and 85 percent of those innoculated reported some type of adverse reaction. That rate was more than double the reaction rate anticipated by the manufacturer in its warning insert, the agency said.

One fifth of the reactions, said the GAO, were ailments more serious than the common report of swollen arms in theinjection area and lasted more than seven days. Most of those surveyed, said the GAO, did not report their adverse reactions to the U.S. Food and Drug Administration's Vaccine Adverse Events Reporting System. Either they were unaware of its existence, concerned about being taken off military or civilian flight duties, or they were concerned about being ridiculed, the GAO said.

At the time of the survey, the GAO said two-thirds of the Guard and Reserve pilots and aircrew members did not support use of the anthrax vaccine, even though most of them were not opposed to vaccines in general. If the anthrax vaccine had been offered on a voluntary basis, said the GAO, 77 percent of the Guard and Reserve members would have refused it.