Fairfax County officials retained a veteran school psychologist despite their knowledge of a 1981 police investigation into allegations that he was sexually involved with a young boy.

The psychologist, Arthur S. Pomerantz, was placed on administrative leave twice before he was forced to resign in July 1984. Last week, Fairfax County police charged him with aggravated sexual battery of a school-age boy in an incident unrelated to the 1981 allegation. His lawyer said Pomerantz will plead not guilty.

Prince William County police, who first investigated Pomerantz when he lived in Woodbridge, said yesterday that in 1981 they had shown Fairfax school officials photographs showing a man they had identified as Pomerantz in a sex act with a boy. Police said they had insufficent evidence at that time to bring charges against Pomerantz.

Fairfax School Superintendent Robert R. Spillane, who said that school officials knew about the police investigation in 1981, Friday ordered school lawyers to recommend ways to tighten screening of school employes.

Spillane, who has been superintendent of Fairfax schools since July 1, said Pomerantz was not fired in 1981 because no criminal charges were filed against him. The psychologist was placed on administrative leave shortly after investigators approached Fairfax school officials and Pomerantz remained on leave until the start of the 1981-82 school year, according to Prince William police and coworkers.

"You can't dismiss someone . . . just because there's an investigation," Spillane said. "He was never arrested or charged. Everyone's entitled to due process."

Pomerantz, 46, who worked as a psychologist in many of the public schools in his 19 years with the schools, could not be reached for comment at his Falls Church home. His attorney, Mark E. Sharp, said Friday his client "denies the charges vehemently. He believes there is no question that his name will be cleared." Sharp said that Pomerantz intends to plead not guilty to the battery charge in Fairfax Juvenile and Domestic Relations Court.

The Journal newspapers Friday disclosed that Fairfax officials knew of the Prince William investigation of Pomerantz in 1981. The police inquiry began when officers received four photographs that had been found in a parking lot and train station near New York City, according to investigator W.P. Metheny.

Two coworkers, who requested that their names not be used, said they had told their supervisors as early as 1974 that they had noticed Pomerantz frequently was in the company of young boys and had requested that he be investigated. They said they were told by their supervisors that the matter would be investigated.

Prince William County police said they had insufficient evidence to bring charges against Pomerantz and the investigation was turned over to Fairfax police after he moved to Falls Church in 1981.

Fairfax police said they renewed the investigation in late 1983 and again approached school officials and Pomerantz's coworkers with the same photographs. In the spring of 1984, Pomerantz was again placed on administrative leave, coworkers said.

R. Warren Eisenhower, personnel director for the county schools, Friday refused to comment on the case, saying that Pomerantz had resigned for "personal reasons."

Complaints about school employes are common, Eisenhower said, and "most of them [are] without grounds. I don't know what we can do other than having some agency do a full criminal check on every employe," he said. "We're a human organization."