Fairfax County school officials said yesterday they were investigating how former Redskin Clarence Harmon, who pleaded guilty to drug charges in Texas in 1983, was hired as a coach and aide at Langley High School this fall.

Harmon told school officials on his job application he had never been convicted of a crime, Warren Eisenhower, assistant superintendent for personnel, said yesterday.

The schools do not prohibit someone with a drug record from being hired, but "we probably would not hire him" if officials had known about the guilty plea, given how recent it was, Eisenhower said.

Harmon said yesterday the drug plea did not make him unfit to work with children. "It happened two years ago and it's over," he said. "Why refresh people's memories on something bad that happened in my life that I regret?"

Harmon, 29, a veteran running back, pleaded guilty in a well-publicized 1983 case to possession of a controlled substance in a Texarkana, Tex., district court. He was fined $5,000 and put on probation for two to 10 years. As of now, he can petition the court to be released from probation.

Under Texas law, he is not considered to have a criminal record, and prosecutor Louis Raffaelli said he could answer "no" when asked whether Harmon had ever been convicted of a crime.

Harmon, released by the Redskins two weeks before his guilty plea, played for the New Jersey Generals of the USFL for two seasons.

Langley Principal James E. Manning said he had not known about the guilty plea, but Harmon is doing a "marvelous job" and "I still think he's a good prospect."

Harmon was recommended to the Langley football coaches by Dan Henning, a former Redskins coach who now is head coach of the Atlanta Falcons. Among Harmon's references was Redskins Coach Joe Gibbs, Manning said.

Manning said if he had known about Harmon's drug plea, he would have mentioned it to personnel officials, or not referred him at all.

But Manning also said, "If he made a mistake once . . . will it follow him to his grave, or what?" Harmon's job includes being an assistant football coach and supervising bus arrivals and departures, Manning said. He said the job pays about $9,000.

The issue of background checks of new employes has become a major issue facing the Fairfax School Board after the arrest of former school psychologist Arthur S. Pomerantz on child sex abuse charges. Superintendent Robert R. Spillane has said he wants to institute criminal record checks of all new employes and current ones too, if possible.