APRIL 12--As the September 11 commission moves on this week to examining numerous FBI and CIA intelligence malfunctions prior to the terror attacks, the below May 1998 memo will surely be cast as another unheeded warning. Generated by an agent in the bureau's Oklahoma City office and titled "Weapons of Mass Destruction," the document warned that "large numbers of Middle Eastern males" were taking flight lessons at Oklahoma airports. That was a development that the agent, also a pilot, thought may have been "related to planned terrorist activity." A similar memo, written three years later by an agent in Phoenix, also spurred little interest in FBI brass. (1 page)