The nuclear power plant disaster at Chernobyl in the Soviet Union showed that humans can survive larger radiation doses than scientists thought, but even so an adequate medical response to nuclear war "is not possible," researchers say.

"Humans can survive considerably greater exposure to radiation than anticipated" with the help of medical treatments tested in the Soviet accident last year, said a report in Friday's Journal of the American Medical Association.

Another study in the same issue, which commemorates the 42nd anniversary of the atomic bombing of Hiroshima in World War II, said long-term health effects of radiation from a U.S. nuclear weapons test in the South Pacific in 1954 were underestimated.

At Chernobyl, more than 90 percent of the 500 people hospitalized with radiation sickness after the accident are now doing well and most have been discharged, according to the report by Dr. Robert Gale.

Two people died instantly and 29 more died of radiation injuries and burns in the months after the accident, said Gale, an American physician who flew to the Soviet Union to help treat victims after the April 26, 1986, explosion.

Scientists had previously estimated that a radiation dose of 450 rads would be fatal to about 50 percent of an exposed population, but some of the Chernobyl survivors were exposed to more than 600 rads, the study found.

Gale said in a telephone interview that he believes doctors could now save humans exposed to about 800 rads using sophisticated treatments that were successful at Chernobyl.

"That's substantially higher than what was previously thought and reflects recent progress in medical care," Gale said. He returns to the Soviet Union periodically to check the progress of the injured.

A rad is a standard unit of measuring radiation exposure. Being exposed to one rad would be roughly equivalent to receiving 50 chest X-rays, said Dave Harward of the Nuclear Management and Resources Council in Washington.

Gale said Chernobyl provided only a hint of what would happen in nuclear war.

"The medical response to Chernobyl, involving physicians and scientists from 20 nations and several million dollars in supplies and equipment, would appear trivial in the context of a nuclear war," wrote Gale.

"An adequate medical response to the intentional use of (even) less than 10 percent of the Soviet or American nuclear arsenals is not possible," said his report.

The Pacific island study said previous reports underestimated by one third the risk of thyroid problems in residents exposed to fallout from a hydrogen bomb set off above Bikini Atoll in 1954.

Dr. Thomas E. Hamilton and colleagues at the University of Washington in Seattle reported they screened residents on 14 atolls and estimated the prevalence of thyroid nodules -- the major health abnormality from the fallout -- in about 2,300 people who were exposed to the blast.

Earlier researchers thought fallout-related abnormalities occurred in only two heavily contaminated atolls. But the new study found abnormalities extended through 12 other atolls, with the prevalence higher in islands closest to the test site.

In the telephone interview, Gale attributed the higher-than-expected survival rate from the Chernobyl accident to the success of several treatments tried for the first time, such as using antiviral drugs to combat infections.

Doctors also found they could freeze a victim's blood platelets immediately after the accident and transfuse them successfully later, when the patient's body had stopped producing new platelets because of the radiation, said Gale, an associate professor at the UCLA School of Medicine in Los Angeles.

At the same time, they found that transplanting bone marrow "can only save a small proportion of victims of radiation accidents," Gale's report said. Eleven of 13 bone marrow transplant patients died, it said.

Another report analyzing lessons from Chernobyl concluded "there are ample medical and radiologic resources in the United States to cope with nonmilitary nuclear accidents."

But the United States must "better identify our medical resources and organize them more efficiently" to respond to an accident like Chernobyl, said the author, Dr. Roger E. Linnemann, a radiation management consultant and associate professor at the University of Pennsylvania School of Medicine.