The chief medical physicist at Malcolm Grow Medical Center at Andrews Air Force Base is being investigated on allegations that credentials he presented for employment are "inaccurate," Air Force spokesmen said yesterday.

Capt. Gul M. Chughtai, a five-year member of the Air Force who calibrates radiotherapy equipment at the hospital, was placed under investigation Thursday by the Air Force Office of Special Investigation. His job does not require a medical degree, and the investigation is "not related to his job performance, which is satisfactory," according to a statement released by base spokemen.

Air Force officials would not say what credentials were under question. Chughtai, reached at his home, said the allegations were baseless and stemmed from a doctoral degree he received in 1983 from Pacific Western University, a school in California that offers degrees through correspondence.

Chughtai said yesterday that he holds bachelor's and master's degrees from Punjab University of Pakistan, which he said is an accredited institution, and that he applied to the Air Force in 1980 based solely on that training. He said he also did graduate work, but did not earn degrees, at New York and Georgetown universities.

"I did not apply that [Pacific Western] degree at all to get any credit from the Air Force," Chughtai said. "It is not an illegal university and the degree is only good in California."

Pacific Western Univesity, in Encino, Calif., is one of "many, many nontraditional, unaccredited, legal colleges" that grant degrees by mail, said Allen Ezell, an FBI special agent in Chapel Hill, N.C., who has investigated such schools.

The FBI has probed diploma mills for years and has sent 7,400 names of buyers of credentials to 11 federal agencies, including the Defense Department, to check against personnel lists.