The Virginia state health commissioner has filed a civil suit in Alexandria Circuit Court against a Northern Virginia radiologist for allegedly buying and operating a CAT scanner without obtaining a "certificate of public need."

The certificate, required under Virginia law for the acquisition of medical equipment costing more than $600,000, is designed to avoid duplicating expensive equipment and curb growing medical expenses.

Dr. Louis P. Kirschner, the head of radiology at Jefferson Memorial Hospital in Alexandria, began operating a CAT scanner in his private radiology practice adjacent to the hospital in October 1983, according to Mark Epstein, assistant director of the Northern Virginia Health Systems Agency.

By state law, the agency determines the public need for medical facilities, equipment and other costly expenditures and then makes a recommendation on their public benefit to the health commissioner.

The CAT (Computerized Axial Tomography) scanner is a sophisticated X-ray machine that photographs soft tissue as well as bone. It is used frequently in the detection of tumors and is more useful than conventional X-rays because it shows the shape of cancerous growths in greater detail. Depending on what part of the body is scanned, each procedure can cost up to a $1,000, according to a spokesman at Alexandria Hospital, where 6,000 CAT-scans were performed last year.

Kirschner, who is the principal owner of the radiology practice named Radiology Associates Ltd., at 4600 King St., could not be reached for comment on the suit. But one of his partners, Dr. Doo Chung, said, "It's none of their damn business," when he heard of the state suit yesterday. "We are a private business. The state should not have any jurisdiction," he added.

According to Senior Assistant Attorney General John A. Rupp, counsel for the State Health Commissioner James B. Kenley, the state law reads that "any institution, place, building, or agency which operates a specialized center or clinic involving CAT scanning services is a 'medical care facility,' " over which the state health commissioner has jurisdiction.

There are 11 CAT scanners in Northern Virginia, only one of which is in a private office, Epstein said, adding that each costs between $500,000 and $1.2 million.

The Health Systems Agency, he said, determined that "it was not necessary for the scanner to be in Kirschner's office," because there were three scanners nearby, at Northern Virginia Doctors, Arlington and Alexandria Hospitals. Epstein said he was concerned that too many scanners would result in higher medical bills.

Lisa Flynn, a Jefferson Memorial Hospital spokesman, said that doctors in the hospital often refer their patients who need a CAT-scan to Kirschner, "for convenience sake because he's right next door."

Kenley asks in the suit that the court enjoin further use of the CAT scanner until Kirschner obtains a certificate of need, which, according to Eptein, is unlikely for a private physician in this area.