Fifty years after the only atomic bombs ever exploded in anger were dropped on Hiroshima and Nagasaki, uncertainties linger about the scope of the weapons' effects.

Tens of thousands of people died -- many horribly from radiation for weeks after the bombings. But "actually, the majority of people in the combined populations of Hiroshima and Nagasaki escaped physically unscathed," said Gilbert W. Beebe, 83, former director of the department of statistics and epidemiology at the National Academy of Sciences, who has studied the medical history of atomic bomb survivors for most of his life.

In addition, of the 300,000 who lived through the bombings and into 1946, Beebe said, "only about 1,500" have died from radiation-caused cancers in 50 years.

"The original fears of other long-term effects like accelerated aging and genetic damage among the survivors and their children have been proven almost entirely unfounded," Beebe said. "It's not at all what most people think."

If Beebe sounds like an apologist for the bombs, he is anything but. He decided long ago that the bombs were "a terrible watershed we crossed in history" and should never have been dropped.

He doesn't like posing as an expert on the bomb, even though Joseph Fraumeni of the National Cancer Institute said "there is no one more important" in the study of atomic bomb effects: "Almost everything we know" about what radiation does to people "comes from studies he helped design."

Beebe and other scientists who have studied the bomb emphasize that nothing they've discovered in the past 50 years suggests the atomic bomb was anything less than a dreadful and apocalyptic weapon, only that the bombs dropped on Hiroshima and Nagasaki -- while horrific -- have proved far more limited in effect than is generally realized. Public perception of those effects, other scientists say, has been commingled with the fears of the far more devastating hydrogen bombs, which now make up the arsenals of the world's nuclear powers.

Japanese and American scientists of the Radiation Effects Research Foundation (RERF) in Hiroshima last year reported that studies of an 86,500-person sample of Japan's 300,000 A-bomb survivors showed the risk of nine different types of cancer increased by some 8 to 12 percent for the 5,000 survivors most heavily exposed. The risk was less among the others, diminishing with their distance and shielding from the detonations. Beebe noted that "the U.S. government has spent well over $100,000 per {radiation cancer} death" in tracking the long-term effects of radiation on the Hiroshima and Nagasaki survivors.

The overall risk of death from cancer among bomb survivors, the RERF said, has proved only 2.5 percent higher than normal.

Japanese and American scientists "settled the question of acute injuries years ago but the public doesn't know that," said Warren K. Sinclair, a biophysicist and former president of the National Council on Radiation Protection in Bethesda, whose nonprofit organization serves as an international clearinghouse for research on radiation safety. Death by the Numbers Anyone puzzling through the maze of casualty figures for the atomic bombs quickly stumbles on one exasperating factor: Almost every source consulted suggests a different toll. The discrepancies among them are often staggering. In August 1945, for example, the Hiroshima prefecture, or local government, listed 32,000 dead from that bomb and another 40,000 injured. Fifty years later the same government and other Japanese sources claim that as many as 200,000 may have died.

Perhaps the most frequently published figure in the United States suggests "from 70,000 to 140,000" died at Hiroshima -- a margin of error of as much as 100 percent.

While the figures for Nagasaki tend to be less erratic, the discrepancies among them indicate even the best are merely a guess where thousands were vaporized in an instant, in many cases with all documentary evidence that they ever existed.

"The exact number of dead and injured {in Hiroshima and Nagasaki} will never be known because of the confusion after the explosions," said the United States Strategic Bombing Survey, published in 1946. "No sure count of even the pre-raid populations existed. . . . The Survey believes the dead in Hiroshima to have been between 70,000 and 80,000, with an equal number injured; at Nagasaki over 35,000 dead and somewhat more than that injured seems the most plausible estimate."

Ten years later, after intense research by a joint Japanese and American commission, the U.S. Atomic Energy Commission published a 477-page volume still viewed by scientists as the most authoritative baseline study of the bombings. Edited by Ashley W. Oughterson, a clinical professor of surgery at the Yale University School of Medicine, and Shields Warren, a professor of pathology at Harvard Medical School, "Medical Effects of the Atomic Bomb in Japan" detailed everything from the hematology and sperm counts among irradiated survivors to the shield effects of concrete and wooden buildings.

To obtain a more exact count of those killed in the bombings, the Oughterson-Warren study calibrated the populations of Hiroshima and Nagasaki at the time of the bombings on the basis of government-issued rice ration cards. A random sample of 5,000 survivors in each city was then questioned about relatives, friends and neighbors killed and injured in the bombings, and that sample, after some adjustment for known variables, was extrapolated for the population at large.

"The best estimate of the population in Hiroshima at the time of the bombing on Aug. 6, 1945, is 255,000 and that of Nagasaki on Aug. 9, 1945, is 174,000," the report said. "By the middle of November {civilian} deaths were approximately 64,000 (25.6 percent) in Hiroshima and 39,000 (22.4 percent) in Nagasaki." Playing Politics? While Japanese and American scientists largely accepted the casualty estimates in the Oughterson-Warren report, other much larger figures have been published over the years, particularly by anti-nuclear activists.

In 1979, for example, a 700-page book appeared in Japan called "Hiroshima and Nagasaki: The Physical, Medical and Social Effects of the Atomic Bombings." It was published by the Committee for the Compilation of Materials on Damage Caused by the Atomic Bombs in Hiroshima and Nagasaki, and included a foreword by the cities' mayors.

The report cited figures forwarded to the United Nations three years earlier by the two cities elevating the bomb tolls to 140,000 in Hiroshima and 70,000 in Nagasaki -- almost double the USSBS and Oughterson-Warren estimates. Unlike the other two reports, however, "Hiroshima and Nagasaki" is clearly an advocacy document, sandwiching medical data among emotional descriptions of suffering, allegations of U.S. censorship, and chronologies of anti-nuclear efforts against U.S. hydrogen bomb tests in the 1950s at Bikini Atoll.

The report explains its boosted death tolls thus: "The Hiroshima City Survey Section investigated the number of casualties until 10 August 1946 and completed its inquiry the following year. The data were then lost and were not discovered for 20 years. . . . Similar data . . . were . . . reported by Nagasaki City."

How such crucial data as the death tolls from the world's first atomic bombs could have been "lost" at the very time U.S. scientists were swarming over Japan to probe the effects of the bombs is not explained. There are veiled suggestions the United States tried to minimize the A-bomb tolls but, said Beebe, "the only real motivation was to find out exactly what the bombs really did. There was an urgency about it for defense purposes as well as purely scientific ones. The whole world needed to know."

The biggest problem, he said, was that while the medical studies of the survivors were in the hands of scientists, "the fatality count was largely in the hands of the Japanese civil authorities, who were basically political. When anyone who had been in Hiroshima or Nagasaki died in later years, they tended -- and still do -- to declare the death due to atom bomb disease.' And of course there is no such thing. Almost everyone died from the bombs because of blast injuries or burns or radiation, and almost all of these were dead by the end of 1945. Our efforts were directed toward determining the exact cause even of apparently normal deaths in later years, so we could tell if the incidence of something like kidney disease was higher among the bomb survivors than among the control populations."

Those efforts were hampered by cultural resistance in Japan to the autopsies necessary to determine the exact cause of death. "Editorials pictured members of the atomic bomb casualty commission as vultures waiting for more bodies to tear apart," said Beebe. In addition, while Japanese scientists were often quite skilled, "the Japanese in the immediate postwar years had no tradition, discipline or training in medical statistics and epidemiology," which led to differences in interpreting data.

There is a further peculiarity about statistics from Hiroshima: The uranium bomb dropped there was unique, unlike the Nagasaki bomb and every atomic bomb tested before or since, which were plutonium. It was thought at the time to have the explosive force of 20,000 tons of TNT. In 1986, however, after decades of comparing its effects with those of test bombs, it was reevaluated at 15 kilotons and the Nagasaki bomb at 21. Thus even as physicists were deciding the Hiroshima bomb was 25 percent weaker than previously thought, Japanese officials were asserting it had killed twice as many people.

The RERF in 1986 also revised both cities' bomb tolls in light of updated population estimates, to 90,000 to 120,000 in Hiroshima (pop. 350,000) and 60,000 to 80,000 in Nagasaki (pop. 250,000). But those figures will continue to be debated, even in Japan, where World War II survivors in other cities note with some impatience that conventional bombings killed hundreds of thousands more people than even the highest estimates attribute to the atomic bombs. 'We'll Never Know ...' Differences over the figures, meanwhile, have been sharpened by the tendency of anti-nuclear activists in and outside Japan to inflate the figures for shock value. On July 7, for example, in an Op-Ed column in The Washington Post, author Kai Bird, co-chairman of the Historians' Committee for Open Debate on Hiroshima, asserted that "official Japanese records calculate a figure of more than 300,000 deaths {at Hiroshima and Nagasaki} -- nearly triple the number of U.S. soldiers killed {in} the entire Pacific War."

Questioned about the source of the figure later, Bird said he had no idea what "official Japanese records" he was citing: He had lifted the 300,000 figure without further examination from an article in the Chronicle of Higher Education.

"My point was to show that all these figures are essentially meaningless," he said.

"We'll never know exactly how many died," said Beebe, "but it doesn't serve truth very well to inflate any of these figures. It's very questionable that after all these years enough serious data would have surfaced to justify such wholesale revision of death statistics published in the 1950s. But of course it's possible."

Beebe retired as a department head years ago only to return "as a worker bee" with the National Cancer Institute, analyzing radiation data on the Russian nuclear accident at Chernobyl. But he keeps up with the ongoing studies of the Hiroshima and Nagasaki survivors and remains a walking encyclopedia of the atomic bomb and its effects.

"It's not surprising that I do," he said. The Bomb "remains the greatest single question of our age." CAPTION: Toshio Terada, 75, still carries scars from the burns he suffered in the A-bomb attack. CAPTION: Hiroshima after the bomb detonation 50 years ago tomorrow: Despite widespread belief that blast effects were catastrophic for survivors, their overall risk of death from cancer has proved only 2.5 percent higher than normal, according to one recent study.