In the early morning hours of Aug. 31, 1957, an Army sergeant named Paul R. Cooper was marched into "ground zero" of a nuclear explosion in the Nevada desert for reasons he believed related to a test on human stress by the Atomic Energy Commission.

This week, 20 years later, the once robust paratrooper died in a Veterans Administration hospital here at 43 of acute myelogenous leukemia.

The disease, he claimed, was inducted by the effects of radiation received from the 44-kiloton atomic bomb blast, code-named "Smoky," at Jackass Flats, Nev. The blast was three times larger than the one that destroyed Hiroshima, Japan, in World War II.

Cooper's death Wednesday came as both Congress and the executive branch were beginning to show concern for the men who took part in the 1950s nuclear tests.

The House subcommittee on health and environment has held two days of hearings on Smoky and has another set for next week.

Meanwhile, the military services have actively begun to track down veterans of the tests. Wednesday, the Pentagon established a toll-free number - 800-638-8300 - to receive calls from ex-GIs. In the planning stage is a long-term study of the effect that radiation at all the atomic tests had on participating soldiers.

Cooper's effort to publicize his plight began last April, when he was confined to a VA hospital in Salt Lake City. He solicited newspaper and television reporters to tell his story, so that "some of my old buddies" who were at the test and who might be in the same shape could help substantiate his claims for VA benefits.

He explained that he was one of a number of soldiers assigned to the nuclear test. Marched first to a trench about 3,000 yards from the device, minutes after the blast they were marched to within "ground zero" of the site, a distance Cooper said was no more than 200 yards.

Cooper died an angry man after a fight with the Army and Veterans Administration. He had been receiving $820 a month in service-connected disability benefits since last April, but only after the VA denied him the money and then reversed itself when he took his case to the public.

And the Veterans Administration Appeals Board, in granting the money, stressed that it had not determined whether Cooper's leukemia was due to the test, but simply that it appeared he contracted leukemia while in the service.

He retired from the Army in October 1972, after more than 20 years service that included three tours of Vietnam. He first learned his leukemia in February 1976.

While his struggle has spawned a congressional inquiry, it has also produced bitterness in his wift.

Normally soft-spoken, she is quick to accuse the Army. "You had better believe they're responsible," she maintains.

She said the three children are taking the death well. "I think they are stronger than I am sometimes."