WASHINGTON - The prospect of mandatory anthrax inoculations has caused a significant reduction in Air National Guard and Air Force Reserve pilot and air crew retention, the General Accounting Office reported yesterday.

The GAO study found that 16 percent of National Guard and Reserve pilots and air crew had transferred to nonflying positions, moved to inactive status or resigned from the service to avoid the shots.

An additional 18 percent of those surveyed by the GAO, the investigative arm of Congress, said they intended to transfer or leave because of the vaccination, which is a series of six inoculations over 18 months.

Of those who had taken at least one of the anthrax shots, 85 percent reported adverse side effects, the GAO found.

The findings could add to the difficulties facing the Pentagon as it prepares for possible military action in Iraq. Guard and Reserve pilots and crew were heavily used in the Kosovo and Afghanistan campaigns and would be expected to participate in operations in Iraq.

Michael Killian is a reporter for the Chicago Tribune, a Tribune Publishing Co. newspaper.