Federal officials have launched a criminal investigation of the Army's 1983 decision to permit the resignation of a former chief of pediatrics at Fort Belvoir even though a subsequent Defense Department investigation found enough evidence of sexual misconduct for a court-martial.

The inquiry will look not only at allegations of sexual impropriety lodged against former Lt. Col. Arthur C. Andreasen, but also at the conduct of his superiors in the Army who allowed him to resign and enter private practice, according to a senior Defense Department official familiar with the case.

The FBI, the Army's Criminal Investigation Division and the U.S. attorney's office in Alexandria are conducting the investigation.

Andreasen, who began private practice at the Kaiser Permanente health organization soon after he left the Army in March 1983, was indicted Jan. 6 by a state grand jury in Alexandria. The indictment charged Andreasen forced a 15-year-old boy to commit sodomy during a physical examination at a private health clinic in Alexandria in 1983.

He resigned from Kaiser Permanente in November.

At a hearing yesterday in U.S. District Court in Alexandria, a lawyer representing Kaiser Permanente asked Judge Albert V. Bryan Jr. to block government attempts to subpoena the records of Andreasen's patients.

"The most important issue before the court is the privacy of the children who were his patients," said Jacqueline Poux, Kaiser's attorney. "If any of those children have been molested, they have already been victimized enough."

Bryan said, however, that the privacy of the children "is probably outweighed by the needs of the government to investigate a federal crime" and urged both sides to compromise. If they do not agree within one week, Bryan said he will grant the government's request.

Federal prosecutors said they have authority to enter the case because the acts allegedly occurred at an Army base. Andreasen's case has been examined extensively in the past by military officials.

In 1984, an internal Defense Department investigation of the Army's handling of the allegations found that his resignation without prosecution could condone the "release of highly questionable physicians into an unsuspecting civilian medical community," according to the Defense Department's inspector general.

The Army has said that procedures in effect at the time were followed in the case.

Defense Department officials confirmed the federal investigation yesterday but would not discuss details. Glenn Flood, a Defense Department spokesman, said it was department policy not to comment on matters under investigation.

One person familiar with the case, however, said that "we are taking a wider look at the way this whole situation has been handled from the start."

The original Defense Department inquiry into Andreasen's resignation found that the Army let the doctor resign from the service without informing civilian medical boards of allegations of sexual misconduct with his patients.

The inspector general's initial report said the Army had evidence against the doctor that included a sworn, detailed statement by a patient who claimed to have been sodomized by Andreasen, a qualified admission by Andreasen and a written opinion from the staff judge advocate that the evidence was sufficient for a court-martial.

The medical command elected to issue a reprimand to the doctor that was not released to civilian medical authorities. His reprimand stated, in part, that "he did not properly counsel a patient who became excited during a genital examination."

The initial investigation was part of an attempt by the Defense Department to create mandatory procedures for reporting allegations of medical misconduct by military doctors to civilian licensing boards.

In 1984, the armed forces began reporting formal disciplinary actions to the National Federation of State Medical Boards.