Bombing Error Puts a Spotlight On Pilots' Pills
American military's long-held but little-known practice of using drugs to keep its weary forces awake and alert, or to help them sleep, becomes focus of attention at military hearing into deaths of four Canadians in airstrike by two American pilots in Afghanistan; Air Force Maj Gen Dan Leaf says decision to take pill is made by individual pilot in the air; lawyers for two American pilots, Majors Harry Schmidt and William Umbach, say men felt compelled to take amphetamine Dexedrine or be scrubbed from their mission, and that drug may have clouded their judgment on night of bombing last April; case brings new scrutiny of amphetamine use in military, although defense's central argument is that pilots should not be held responsible because they were not informed that ground fire they spotted near Kandahar was Canadian military exercise; government argues that Schmidt ignored order to hold his fire, and that Umbach, lead pilot, failed to exercise good leadership; photo (M)