A team of U.S. and Israeli doctors is performing bone marrow transplants on victims of the Chernobyl nuclear accident, the scientific director of the Milwaukee-based International Bone Marrow Transplant Registry said yesterday.

Dr. Robert Gale confirmed that the high-risk operations were under way during a telephone call from Moscow yesterday morning to Dr. Mortimer Bortin, professor of medicine at the Medical College of Wisconsin and scientific director of the registry.

Transplantation of the bone marrow, the body's "blood factory," is the only effective treatment for marrow destruction by severe radiation poisoning, which many experts believe could afflict people at or near the Chernobyl nuclear plant during the accident.

Success of the transplant depends on extremely precise matching of blood types between donor and recipient.

Gale, chairman of the registry's advisory committee and a member of the bone-marrow transplant team at UCLA Medical Center in Los Angeles, flew to Moscow last Friday. He was joined this week by two UCLA colleagues, Dr. Richard D. Champlin and Dr. Paul I. Terasaki, and Dr. Yuri Reisner of the Weizmann Institute in Israel.

Bortin said Gale did not indicate how many transplants had been performed or estimate how many Soviet citizens were injured. An explosion April 26 triggered an apparent meltdown in a reactor whose graphite core burned for several days.

Bortin and other American doctors speculated that Gale chose not to discuss such estimates to avoid embarrassing Soviet officials and jeopardizing the international effort to help accident victims.

Terasaki, director of UCLA's tissue-typing laboratory, is setting up a similar laboratory to help Soviet doctors match transplant patients with potential marrow donors, Bortin said. Reisner, an expert on T-cells, which play a key role in the body's immune system, is separating such cells from donated marrow to reduce the risk of rejection. Champlin, director of UCLA's marrow transplant program, and Gale are performing the transplants.

The operation's major risk is that the recipient's immune system will reject the donated marrow -- or that the donated marrow will reject the recipient's tissues. Without healthy bone marrow, the body cannot produce enough blood cells to ward off infection and sustain life.

The international marrow registry, which includes 128 medical centers that perform marrow transplants in 60 countries, hopes to collect detailed data on the transplants performed in the Soviet Union. Such data could help doctors treat victims of any future nuclear accident, Bortin said.

The registry also has access to a list of more than 50,000 potential marrow donors, filed by blood type.

Bone marrow transplants also are used to treat some patients with leukemia or aplastic anemia.