The former chief of anesthesiology at Walter Reed Army Medical Center, a colonel who pleaded guilty two years ago to taking money from drug companies for tests done on Army time, has been granted permission to resume his practice at the hospital, Army and hospital spokesmen said yesterday.

But Wednesday, the day after his credentials were restored on recommendation from a review team at the hospital, Dr. Robert L. Watson went on leave, according to spokesmen.

Watson could not be reached yesterday for comment.

He had not practiced at the hospital since an investigation of his dealings with the drug companies began in 1983, but was kept on the payroll, hospital spokeman Peter Esker said.

Watson, a 20-year veteran, has asked to retire Jan. 31 from the Army, according to Army spokesmen. Whether he will be granted that retirement at his current rank -- and receive a retirement pay of half the base pay for a colonel of $45,270 -- is a decision still to be made by an ad hoc Army review team, which recommended late last year that Watson be dismissed from service, an Army official said.

Watson, 50, asked for the retirement in lieu of dismissal, according to Elaine Henrion, an Army spokesman. The restoration of Watson's credentials means that the Army will not refer the case to the medical board in Virginia, the state in which Watson is licensed, Henrion said. A representative of that board said, however, that Watson's record already is being investigated and was submitted yesterday for review by the state attorney general's office.

Watson was granted "provisional credentials" Tuesday by the hospital's commanding officer after a review team there met twice last week, voting once to refuse the credentials and then a day later, after an appeal by Watson, agreeing to grant him the credentials, Esker said yesterday. "Provisional credentials" are standard credentials given to new doctors and need to be reviewed by the hospital in 90 days before becoming permanent. Permanent credentials are granted on an annual basis.

Watson's credentials had lapsed since he was investigated by the Army and FBI in 1983 and later pleaded guilty in U.S. District Court on charges of taking $4,000 from drug companies to test drugs while he was working for the Army, Henrion said.

Watson entered the plea on the grounds he would not be prosecuted again in connection with the charges, Esker said. Watson was fined $5,000 and sentenced to five years' probation.

Watson was subsequently recommended for court-martial by the commander of Walter Reed hospital, a spokesman there said, referring to hospital records. The court-martial convened and then was dismissed in May 1984 when it was ruled that the Army was an arm of government and its prosecution would violate the District Court plea agreement, Army spokesmen said records show.

Watson's clinical privileges were not reviewed by the Army's quality assurance program in 1983 and, although he retained his salary, he was not allowed to practice at the hospital, Esker said.

An Army review board, consisting of three senior officers, met last October to review Watson's status, according to hospital officials. That board recommended he be dismissed from service. Following Army procedure, Watson had the right to request retirement in lieu of dismissal, Henrion said.

Henrion said yesterday that "one of the matters that will be decided is whether he is busted" from the rank of colonel. A drop from colonel to lieutenant colonel would mean a loss of $360 a month from the $3,773 a month that a colonel of Watson's tenure would earn. Since retirement is half pay, Watson could lose $180 a month if he is dropped one rank, according to Army figures.

Virginia officials said Friday that a review of Watson's record began after the federal charges were brought against him.

The medical board, which licenses physicians and has the authority to revoke licenses, was researching the court martial charges and will forward the information to the state attorney general's office for review, said Stephanie Sivert, deputy administrator for the board.