The Virginia State Board of Medicine revoked the license yesterday of a Loudoun County doctor who repeatedly "prescribed treatments which have not been shown to be safe or effective or consistent with acceptable medical practice," the board said in its findings.

The 14-member board, which sits in Richmond, also found that the physician, Thomas J. Roberts, "aided and abetted" a doctor not licensed to practice in Virginia. Roberts was "grossly ignorant or careless in his practice or has committed gross malpractice with regard to those patients," the board said in its findings.

The board said that permitting an unlicensed person to practice medicine is so "grave" that it alone would justify revocation of Roberts' license, according to the board's 30-page finding. But the main issue during the Leesburg doctor's revocation hearing, which began late last year, was how he practiced medicine.

A 1960 graduate of the University of Virginia medical school, Roberts acknowledged that some of his treatments--which included grapefruit and coffee enemas and injections of solutions designed to cleanse the body--could be called "experimental." Neither Roberts nor his lawyer could be reached for comment yesterday.

In 1979, doctors at Loudoun Memorial Hospital questioned Roberts' competence, which led to the suspension of his privileges there.

David Hathcock, director of information and programs for the state's Attorney General's Office, which investigated Roberts for the board inquiry, said the board paid close attention to the treatment Roberts prescribed for six of his patients, two of whom died.

One of the six patients was Stephen Ours, 33, who died of cancer Dec. 31, 1981, and whose treatment by Roberts was a central issue in the state's investigation of Roberts.

In late 1980, Ours went to Roberts, complaining of a slight recurring fever. Ours' wife Karen told the board that her husband was tired of doctors after complaining to them for years about the problem.

After tests, Roberts told Ours that his fevers were caused by a malignant tumor deep in his chest, and recommended conventional radiation treatments. Ours' mother, Eloise Ours, testified that Roberts then helped her son in combating his cancer with a diet of carrots, burdock roots, whole grains and collards after Ours refused radiation therapy.

The board found that in the Ours case, Roberts had acted improperly. According to the board, when Roberts' treatment of many of his patients was considered, "a pattern of gross ignorance and carelessness. . . " emerged that was so serious it warranted the revocation of Roberts' license to practice medicine.