Former Redskin Clarence Harmon resigned yesterday as a coach and aide at Fairfax County's Langley High School after school officials discovered he had pleaded guilty to a drug charge in Texas two years ago.

Harmon, who was hired this fall, told R. Warren Eisenhower, assistant superintendent for personnel, that "he did not want to go back through that unfortunate incident, and rather than do that, he resigned," said Dolores Bohen, county school spokeswoman.

Bohen said Harmon's resignation would end the school system's plans to investigate the veteran running back's involvement in the well-publicized drug case.

"You're not going to investigate him now that he's resigned," Bohen said.

Harmon could not be reached for comment yesterday.

Bohen said she did not think school officials planned to look into hiring procedures to determine why they did not know about Harmon's guilty plea to a charge of possession of a controlled substance, for which he was fined $5,000 and given two to 10 years probation.

Under Texas law, Harmon, 29, does not have a criminal record.

"Right now we're very conscious of this business of background checks, but how would we have known about Harmon ?" Bohen said.

Fairfax County officials now have access only to Virginia criminal records.

The issue of background checks on employes is now a top priority with school officials, prompted by the recent arrest of a former school psychologist, Arthur S. Pomerantz, on child sexual abuse charges.

Both Eisenhower and Langley High School Principal James E. Manning said they did not know about Harmon's guilty plea before they hired him, despite extensive press coverage at the time. Harmon was paid about $9,000 a year.

But several Langley students and parents said Harmon's past was common knowledge around the McLean school. "We all knew of his background . . . and we pretty much assumed the administration did, too," senior David Abner, 16, said yesterday.

Beth Scott, 16, a junior and football team manager, said the football team was organizing a telephone campaign to get Harmon rehired.

A letter asking Harmon not to resign was signed by 85 members of the football team and coaching staff and mailed yesterday to him, to school officials and to School Board members.