Fairfax County School Superintendent Robert R. Spillane yesterday backed off his statement of last week that school officials correctly handled the case of a veteran school psychologist who was allowed to continue in his position in 1981 while he was being investigated on allegations of child sex abuse.

"I shouldn't have come to that conclusion," Spillane said, referring to his statement that school officials did not have enough evidence to dismiss the man. Spillane announced yesterday that county officials will conduct an investigation into the handling of the case.

School officials have said they knew in 1981 that police were investigating allegations that psychologist Arthur S. Pomerantz, 46, was sexually involved with a young boy. His coworkers said they first voiced suspicions about him to superiors in 1974. Pomerantz was twice placed on administrative leave, but returned to a job counseling troubled youths in 1981-82. He was forced to resign in July 1984.

No formal charges were brought against Pomerantz until Aug. 16, when Fairfax County police charged him with aggravated sexual battery of a school-age boy in an incident unrelated to the 1981 allegation. His lawyer, Mark E. Sharp, said he will plead not guilty.

Yesterday, John F. Herrity, chairman of the county Board of Supervisors, said the psychologist could have been fired, and the president of one of the county's two teacher associations said he should have been removed from direct contact with children.

Spillane said his earlier expressions of strong support for the school system's actions were based on incomplete information. He said he wants to review the evidence school officials had before deciding whether they should have taken stronger action.

"If in fact we had something . . . then I can make some decisions," said Spillane, who became Fairfax County superintendent July 1.

Spillane said over the weekend that the schools could not have dismissed Pomerantz without a formal charge by police.

Herrity disagreed yesterday. "You don't have to be convicted before you're bagged as an employe," he said. "I don't believe what the school system is doing now is adequate or makes sense.

Spillane and County Executive J. Hamilton Lambert said they are launching a joint investigation of the Pomerantz case, which Lambert said probably will involve the police.

"We're going to look at all aspects of it," Lambert said. He would not say how long the investigation might take.

The investigation's scope is expected to include whether the schools could have taken stronger action against Pomerantz, whether personnel policies should be changed, and how new employes can be screened.

R. Warren Eisenhower, assistant school superintendent for personnel, said the county ran FBI fingerprint and criminal records checks in 1965, when Pomerantz was hired, but "that wouldn't have helped us in this case" since the man had no criminal record. The FBI has since discontinued the service, he said, and Virginia law permits checks only of state police records.

Rick Nelson, president of the Fairfax County Federation of Teachers, criticized the school system for putting Pomerantz back in contact with students. Nelson said he knows of cases in which teachers were fired for lesser offenses than Pomerantz is alleged to have committed. "The fact is, they had the power to [fire him]," he said.

Kevin P. Dwyer, a Montgomery County school psychologist who leads the state's delegation to the National Association of School Psychologists, said Fairfax officials could have asked his group to investigate Pomerantz for violating its ethics code. If wrongdoing had been found, school officials would have been notified, he said.