The studies on the effects of radiation were part of a programme carried out by the CIA between 1953 and 1967 according to Steven Aftergood of the Federation of American Scientists. He said it would be impossible to find out the exact number of radiation victims 'because the CIA destroyed a large part of its records in 1973'. Some tests were conducted without the consent of subjects, and some reportedly occurred as late as the 1970s.
The CIA did not attend a meeting convened by Mr Clinton at the White House on Monday, which set up a fact-finding body to to look into the radiation experiments. Its destruction of old records in 1973 may have been to pre-empt investigation by Congress at a moment when the agency was under increasing attack.
In Washington at least 10,000 people a day are telephoning a special Energy Department hotline to establish if they were affected by the tests. Detailed revelations about testing by the US Energy Secretary, Hazel O'Leary, coming after years of official details that anybody's health has been damaged, have alarmed many people who believe they might have been unwitting victims of the experiments.
The White House is still wary of saying they will be compensated, but President Bill Clinton says something should be done 'if Americans are deemed to have been wronged'.
Little of the information is entirely new but, for the first time, the identity of many of the victims has been revealed, dramatising what happened and fuelling media interest. In the small town of Italy in Texas, for instance, neighbours thought that Elmer Allen, an alcoholic former railway porter who had lost a leg, was mad because he claimed he had been 'used as a guinea pig' in a government experiment.
Diagnosed a paranoid schizophrenic, Mr Allen's ravings were dismissed until last month the Department of Energy revealed that he was telling the exact truth. According to his medical records he was injected with plutonium - along with 17 others - by doctors in San Francisco on 18 July 1947, three days before his leg was amputated because of bone cancer. Doctors never told him the nature of the experiment.
As late as 1986 a congressional committee which produced a report, entitled American Nuclear Guinea Pigs: Three Decades of Radiation Experiments on US Citizens, was greeted by government disapproval and press apathy. The issue only reignited last November when a local newspaper in New Mexico, the Albuquerque Tribune, used the Freedom of Information Act to identify by name Mr Allen and other victims of the earlier experiments.
Ms O'Leary said: 'My expectation is there will be more disclosures. Almost every 36 hours we're learning more.' Experiments so far disclosed include tests on retarded teenagers at a school in Massachusetts who were given radioactive milk with their breakfast cereal, and pregnant women who took radiation pills to see what effect radioactive iron would have on the foetus. A scientist who injected seven baby boys in Memphis, Tennessee, with radioactive iodide said: 'Naturally, we hoped there was no damage.'
The experiments, almost without exception, involved using as guinea pigs people who, even if they were told what was happening to them, were not well placed to refuse to
co-operate with doctors. They were usually poor, black, elderly, prisoners or hospital patients suffering from serious illnesses. A doctor's report on one patient, injected with radioactive salt to see the effect on his kidneys, says: 'As he had no home, he agreed willingly.'
In the 1940s, ignorance of the effect of radiation might explain the willingness of the government to subject people to it - though as early as 1950s one doctor said in a memo that there was 'a little of the Buchenwald touch' about what the Atomic Energy Commission was doing. But by the 1970s, the experimenters were conscious of the need for secrecy. An internal memo from the laboratory which dealt with Mr Allen and other victims warning doctors never to use 'the word plutonium in regard to these cases'.