KANSAS CITY, Mo. (AP) _ An investigation into allegations of drug use by air traffic controllers at a suburban flight control center apparently stems from a Labor Day farewell party for one worker, controllers say.

Five controllers have been temporarily removed from duty, and as many as 30 or more of the 350 controllers at the Air Route Traffic Control Center in Olathe, Kan., reportedly have been questioned or tested for drugs.

Three current or former controllers at the center who requested anonymity said the investigation apparently began after a party-goer told the Federal Aviation Administration that marijuana was smoked at the party.

FAA spokeswoman Evelyn Siro declined comment on the reports Friday.

''There's no reason at all for the traveling public to be insecure,'' Ms. Siro said. The Olathe center directs more than 5,000 aircraft daily in the Midwest.

She said an unspecified number of urine samples had been sent for testing to a North Carolina laboratory. She declined to comment on whether results have been received since the first controller was put on leave Sept. 12.

Two controllers have complained to the American Civil Liberties Union about how the investigation is being conducted, said Dick Kurtenbach, ACLU director for western Missouri and Kansas. He said the controllers believe the investigation seems to be based on friends and acquaintances, rather than job performance.