An English scientist has published results of a new study indicating that the medical effects of the 1945 atomic blasts at Hiroshima and Nagasaki--and of high-dose radiation generally--may be much greater than is generally believed.

The scientist, Dr. Alice M. Stewart, reexamined data about survivors of the atomic bombings from 1950 to 1974 and concluded that deaths in that group from radiation effects were more than 10 times higher than previously reported.

Some American researchers, however, criticized her work and said her arguments were not substantiated. Her study was supported by the Environmental Policy Institute in Washington.

This is an intensely controversial question in science, and experts for years have debated the health risks of radiation. The issue is of practical importance because safety standards even for low-level radiation--involving everything from nuclear reactors to microwave ovens--are derived partly from knowledge of the Japanese blasts.

The puzzle for researchers was that, when someone from Hiroshima or Nagasaki died five years after the bombings, it was not always apparent whether the death was a delayed effect of radiation. The Radiation Effects Research Foundation had reported that, of 80,000 people exposed to the atomic bomb blasts and still alive in 1950, only 415 died from delayed effects of the bombings, all from cancer.

Stewart examined records of that same group and concluded that at least 4,400 deaths resulted from radiation effects. Her article appeared in the June issue of the British Journal of Epidemiology and Community Health, and was reported in the June 19 issue of the Washington-based Science News.

Except for cancer, the death rate of the five-year survivors of Hiroshima and Nagasaki was similar to that of other Japanese. This had led earlier studies to conclude that cancer was the only significant delayed effect of the bombings.

But Stewart argued that there were two additional effects that tended to cancel each other out and so were not easily noticed. First, the 80,000 survivors in the sample should have been unusually rugged and healthy since they were the ones who did survive. This would give them a lower death rate than the average. Second, those survivors suffered disabilities such as bone-marrow damage that weakened their resistance to disease and wiped out the advantage of their previous healthiness.

Stewart showed that the group had a high number of deaths from aplastic anemia and other blood diseases, with those exposed to the most radiation the most likely to die. On the other hand, causes of death that clearly were unrelated to radiation--such as cerebral hemorrhages--were 30 percent less common in the Hiroshima and Nagasaki group than for other Japanese. She concluded that those exposed to radiation were more likely to die from other diseases.

Seymour Jablon, a statistician with the National Academy of Sciences in Washington, said Stewart had made assumptions that were not backed by evidence. He said there is no indication that "healthy survivors" of a nuclear blast would start out with any greater immunity to cancer, and he noted that there is no proof that radiation causes aplastic anemia.

Charles E. Land, a health statistician with the National Cancer Institute whose earlier work suggested that survivors of the Hiroshima and Nagasaki bombings were not particularly prone to infectious diseases, also criticized Stewart. He said she had made unwarranted assumptions and presented arguments that were largely untestable.