An American AIDS patient treated with a novel combination of therapies to boost his immune system is "doing well" 10 months later, a top National Institutes of Health official reported yesterday.

Dr. Anthony Fauci said the highly experimental approach, involving use of a virus-fighting drug, a bone marrow transplant and special immune cell transfusions, was promising because it demonstrated "the feasibility that you can reconstitute the immune system of someone with AIDS. Prior to this all attempts were complete failures."

Although he said it is the "first time" researchers have shown a sustained response in their attempts to restore the damaged immune system of a victim of acquired immune deficiency syndrome, Fauci cautioned that another year of follow-up is needed before it could be considered a success.

"It's not a breakthrough. We haven't cured anybody yet. This has shown the principle" can work, said Fauci, director of the National Institute of Allergy and Infectious Diseases. He was interviewed by telephone from Paris, where he spoke yesterday before an international meeting there on AIDS.

AIDS is caused by a virus that can destroy white blood cells, specifically T4 lymphocytes, that are a crucial part of the body's defense mechanism. There is no proven treatment or cure for the deadly disease.

Scientists from the Walter Reed Army Institute of Research in Bethesda also reported in Paris yesterday on the latest statistics on AIDS infection among American military recruit applicants.

A spokesman here said that 305,000 potential recruits tested over a six-month period starting in October 1985 showed an infection rate nationally of 1.5 per 1,000, about four times that among blood donors. Such recruits tend to be sexually active young men who might be at greater risk. Those found "positive" on extensive blood tests are rejected for military service.

Fauci reported on three AIDS patients who received bone marrow transplants last fall from their healthy identical twins. "Two of the three are not doing well . . . . One of the three is doing very well 10 months later," he said.

The AIDS patient, a man in his early 30s who suffered from a cancer called Kaposi's sarcoma, received an antiviral drug and transfusions of lymphocytes before undergoing a bone marrow transplant from his identical twin brother.

Since then, Fauci said he has continued to receive regular transfusions to boost his immune defenses until the transplanted bone marrow can produce such cells on its own.

Thus far, the patient's immune system tests have shown measurable improvements, he said, including a "dramatic increase" in T4 cells and lymphocyte function. No signs of the AIDS virus remain in his blood, he said, and it appears that the Kaposi's cancer in his lymph nodes has "stabilized."

Fauci said that the transfusions will continue for another month or two, and then the patient, who is out of the hospital, will be observed over the next year to see whether his immune system continues to function well on its own.

If the approach proves successful, he said, bone marrow transplants with matched relatives could be considered. But he said it is premature for other AIDS patients to seek bone marrow transplants.