The American Medical Association is screening credentials of all doctors in the Army, Air Force and Navy in an attempt to determine whether physicians who have been disciplined or have fake diplomas are serving in the U.S. military, the association confirmed yesterday.

The mass screening of about 18,000 active and reserve medical officers has turned up 29 doctors in the Army and Air Force whose licenses to practice have been revoked or suspended, according to Dr. James Todd, senior deputy executive vice president of the AMA.

An Air Force spokesman said five of the disciplined doctors are Air Force employes but did not say whether they are civilians. "One who did not have another valid license has been suspended," said Pat Bragg, Air Force assistant for public affairs, who said the doctor had been practicing in Germany. All five had licenses when hired, she said.

The other four lost their licenses in one state but have valid licenses in others, she said. These doctors are being checked by committees at Air Force hospitals where they work to "see whether they should keep their privileges," she said.

An Army aide said the AMA checked credentials of 6,000 Army doctors but could not determine what the Army is doing about those found to have licensing problems.

The surgeons general of the Army and Air Force requested the screenings last June and were given the results in January, according to the AMA. The Navy did not ask for such screenings until February, Todd said, and the review is to be finished next month.

The AMA has a computerized "Physician Masterfile" containing 600,000 names. It tracks doctors from medical school throughout their practice. It receives nearly all of its disciplinary records from the National Federation of State Medical Boards, which relies on members to report actions it takes against doctors.

Hospitals, state boards and individuals may request a doctor's file from the AMA but are not told whether a doctor has been disciplined. Instead, those inquiring are told to contact the state board where the action occurred.

"It is couched in terms that 'they need more information,' " Todd said. "My impression is the message gets through . . . . It's better they learn it from the state board, because we are once or twice removed from the initial action."

The discipline files contain many gaps because many states have not reported or have reported sporadically for years. Further, most states do not tell the AMA or the federation when a doctor voluntarily surrenders a license, an action that many doctors take to avoid disciplinary proceedings.

The files also do not contain the actions of most hospital boards. For example, neither discipline file mentions the New Jersey hospital that asked Dr. Donal Billig, a former heart surgeon at Bethesda Naval Hospital, to leave the staff because of questions about his competence.

"If states don't report, we don't get it," said Dr. Bryant Galusha, director of the federation. Although Rhode Island, the District of Columbia, Delaware, Guam, Puerto Rico and the Virgin Islands failed to report in 1984, he said, this represented the most complete reporting in the federation's 73-year history.

The Defense Department began reporting its disciplinary actions against doctors to the federation in 1981, but other large government employers of doctors, such as the Veterans Administration, do not, Galusha said.