A federal judge yesterday ordered the head of anesthesiology at Walter Reed Army Medical Center to serve five years on probation and to pay a $5,000 fine for receiving illegal outside income from two drug companies.

Col. Robert L. Watson, a 19-year Medical Corps veteran who has been chief of anesthesiology at Walter Reed since 1979, pleaded guilty last month to receiving $4,000 from the drug companies in connection with drug studies approved by the Army and carried out by Army personnel at Walter Reed, according to documents filed by assistant U.S. Attorney Noel A. Kramer. There was no evidence presented that Watson's income from the companies influenced the outcome of the studies, according to the documents.

At a hearing yesterday, Watson's attorney, Robert Patterson, told District Judge Louis F. Oberdorfer that Watson "made mistakes in judgment . . . and admits he was wrong." Patterson said Watson, who faced up to two years in prison, had an outstanding military record, and that "this is the only blemish on that record." Patterson said Watson still faces possible disciplinary action by the Army and by medical licensing authorities.

Oberdorfer ordered documents in the case to be forwarded to the Army and medical licensing officials.