The chief of a heart surgery unit at Bethesda Naval Hospital has lost his right to practice there after questions were raised about his professional competence, and hospital administrators have begun a formal investigation to determine how he was hired and allowed to practice in the Navy.

Cmdr. Donal M. Billig, whose clinical privileges were suspended in November, was notified last week that his staff appointment as head of the cardio-thoracic unit as well as his surgery privileges were revoked, said Lt. Alan Goldstein, a Navy special assistant for public affairs.

Goldstein said the action was based on the recommendation of the hospital's credentialing committee. Billig, 54, continues to work as an administrator for the Navy's Physical Evaluation Board, also at the medical complex in Bethesda.

Goldstein would not say yesterday what specific event prompted Billig's suspension. But he discounted allegations that the physician's patients had a high mortality rate -- meaning that too many patients in his care died.

"His morbidity and mortality rates were within national standards," Goldstein said. "The issues can go beyond morbidity and mortality."

Neither Goldstein nor spokesmen for the naval hospital would explain what charges Billig faced or what medical data was used in the credential review March 4. They also would not explain why a separate investigation into the hiring of Billig was being conducted.

Attempts to contact Billig through the Navy and at home were unsuccessful.

According to Navy records, Billig holds licenses in New York, Texas, Massachusetts and Pennsylvania.

Medical boards in New York, Texas and Pennsylvania confirmed he holds licenses in their states. But a representative of the state medical board in Massachusetts said he once was licensed in 1968 but she could find no record of a current license.

New Jersey officials said Billig once held a license there but retired in 1981 after an inquiry was made by Monmouth Medical Center in Long Branch, N.J., where he then practiced. Based on the medical center's information, a prelimiminary inquiry was begun by the state medical board there.

Representatives from the Monmouth medical center, located about 50 miles south of New York City, would not elaborate on their experience with Billig but said they notified state medical officials after an incident of "questionable surgery."

New Jersey state medical officials would not comment and said the board dropped the investigation after Billig retired.

As part of the surrender of his license, Billig agreed not to practice in New Jersey, state officials said.

In December 1982 Billig was commissioned by the Navy. He was made a staff member at Bethesda Naval Hospital in January 1983 and became head of the department there in June 1983, according to Navy records.

Defense Department regulations require that all doctors, before they are hired by the military, have their credentials scrutinized. Naval officials said yesterday they did not yet know whether a review was made of Billig's license. "That is part of the investigation," Goldstein said.

Billig did not list New Jersey as a state in which he was licensed at the time he applied, Goldstein added.