LeOra Hafen remembers well the day in 1956 that her 15-year-old daughter died. It was back in the days of the U.S. government's atomic bomb tests 100 miles west of here, days when her daughter would walk home from school oblivious to the mushroom cloud forming a state away.

"She was on the sofa," recalls Hafen, "and she cried, Momma, call Dr. Kon. I'm gonna die.'

Why, Karlene," Hafen tried to reassure her, "you are not either."

"Yes I am Momma," replied the pretty girl, who was in her final and fatal moments of acute leukemia. "This room's just full of angels." And she closed her eyes and never moved again.

Only a month earlier, Karlen's uncle Paul, a rancher with the look of a Marlboro man, had been diagnosed as also having leukemia. Paul Hafen was a cowpuncher, rode hard, sometimes for weeks on end, to move his cattle across the rangelands of nearby Arizona, where at least once he got caught in broad daylight under the dust of a test blast cloud.

But Hafen somehow survived his leukemia until the spring of 1963, and, after his death, Max Brinkerhoff, a rancher friend out on that Arizona grazing land, began helping Hafen's widow Helen, run the ranch.

Last Feb. 27 Max Brinkerhoff also died of leukemia. He was the fourth in a group of schoolboy chums - the others were LaVier Tait, Gayneld Mackelprang and Gail Heaton - to die of leukemia.

A collective coincidence of individual and random tragedy?

Or do their deaths, and those of so many others across this region of mesquite and mesas, represent civilian casualties of atomic weapons people killed by their government at it tested the arms that were supposed to protect them?

From 1951 until the nation's bomb testing was moved underground in 1962, 87 above-ground nuclear tests were conducted at the Nevada proving grounds, west of here. Dr. Joseph Lyon, who runs the Utah State Cancer Registry, says that 20 to 26 of those tests sent fallout clouds into Utah.

While the southwestern part of the state received heavy fallout, wind currents carried radio activity over an area stretching from the Grand Canyon almost to Salt Lake City. Some 20,000 people lived in the Nevada, Arizona and close-in Utah areas alone.

The true extent of any health problems is virtually unknown: the government has long maintained that there have been no adverse effects but then no long-term or widespread study has ever been conducted here despite leaders of controversy.

But many of the people whose deaths or illnesses were examined by The Washington Post in the last month shared the common experience of having been out of doors when dark blast clouds moved overhead, and their friends and families have few doubts of the relationship between those clouds and subsequent illnesses.

"I remember one time, against a hill here in Hurricane [Utah], somebody, my mother or father, saying, 'Look, you can see the cloud'" recalls Jimmie Humphries, 30. Eleven days ago his 32-year-old brother Randy, a highway patrolman, died of leukemia.

Randy, Jimmie and other family members attribute the leukemia to the test blasts, and when the disease was diagnosed last summer they all joined the many others here who had long been convinced that the A-bombs were shortening the lives of many people here.

That fear has only been heightened by recent disclosures of leukemia among soldiers present at a 1957 test blast, "Project Smoky."

They are not alone, President Carter in May assigned the Department of Health, Education and Welfare to examine the effects of low-level radiation on participants in nuclear tests and workers in government nuclear facilities, citing those leukemia cases among soldiers.

In addition, HEW soon is expected to begin a high-priority reopening of the only major investigation ever conducted into the health effects of nuclear testing on civilians, which involved 2,000 schoolchildren in two southern Utah counties here.

That '60s investigation, which officials at the time acknowledged may have stopped too soon, found no adverse impact on the youngsters tested for thyroid abnormalities. Despite the admitted limits of the investigation, it has always been relied on by nuclear testing officials as proof of the safety of the nation's test activities.

But even a renewal of the HEW effort would fall short of the widespread investigation that one radiological health expert at the University of Utah says is warranted in light of the soldiers' leukemia.

"We had a whole damn region subjected to one after another of these fallout patterns over a long period of time," said Dr. Robert L. Pendleton, "and some of [the radiation] was rather high.

"There's a lot of potential health damage ticking like a bomb," he said, "and nobody's even trying to find out if there's a problem."

Both Pendleton and Dr. Dan Hoffman, an epidemiologist with HEW's Bureau of Radiological Health, also cite the 10-year-or-more delay in the appearance of thyroid abnormalities, some of which were cancerous, among residents of a Pacific island downwind of test blasts there.

Those exposed on the island of Rongelap were accidentally covered with radiation in 1954, during atomic testing on the island of Bikini, 110 miles away, when the wind shifted just before detonation.

A year before that, on May 19, 1953, a wind shift at the time of the "Project Harry" test blast in Nevada sent an unusually hot cloud over this city, which then had a population of 4,500. Traffic was blocked, and residents were told to stay inside for hours.

Marden Brown, a painter, still remembers the Atomic Energy Commission officials washing down his half-ton blue GMC pickup truck that day, rinsing it repeatedly, trying to get all of the radioactivity off.

About 10 years later, Brown said, his malignant thyroid gland was removed.

"Harry" also possibly caught Helen Reichmann, who was out working in her garden one day about that time. Suddenly she became ill and, vomiting and feeling weak, she left her garden to lie in bed. According to her son, Lawrence, a doctor, only then did she hear on the radio the warnings to stay inside because of fallout.

She died last February of cancer, which apparently started in her stomach. "Medically, I don't know," says Dr. Reichmann about whether his mother's death was caused by the atomic tests. "But emotionally - yes, I do think so."

Those whose lives have been touched by the cancer deaths here are unanimous in their opinion that the cause was the testing, but the emotional response is varied.

There is the fear expressed by Darrell Nisson, whose 13-year-old Sheldon died of leukemia in 1959, that the human race is destroying itself. He had recognized the look of leukemia in his son after having watched 9-year-old Jessilyn Turner, two blocks away, die of leukemia.

There is the frustration felt by Stanford Staheli that lives have been lost here to develop weapons that went unused when they could have ended wars. Thus, he says, the death of his son, Mason, of leukemia in 1959, was "pretty much in vain."

There is the outright bitterness of Jimmie Humphries, who says,: "I'll tell you, I've been in the National Guard for 12 years and (now) it's damn hard to go down there and put that uniform on, and if I didn't think someone had to protect this country, I wouldn't do it anymore."

There is also the effort to forget, to blot out the excruciating events of death. Lorna Bruhn does not even care to remember the year her husband, Arthur, then president of Dixie College here, died of leukemia. The college puts the date as July 5, 1964, less than a month before Gayneld Mackelprang's death.

There is, too, the unavoidable sense of having been cheated out of life. "It has cost me my life, practically," says Vonda McKinney, whose husband, Len. died of leukemia in 1962. "Everything my husband and I had worked for for 20 years was lost. For seven years I was walking around in a state of shock."

The McKinneys live out along that same stretch of Arizona rangeland near Fredonia, where Paul Hafen and Max Brinkerhoff ran livestock, where Gail Heaton cleared land for grazing until he died last November, where LaVier Tait worked loading logs on to trucks until his death in 1975, and where MacKelprang a school superintendent, used to hunt rocks in the valleys and in the mountains.

It is also the place where Odessa Burch could look out her bedroom windown in Fredonia and see the dust clouds from the bomb blasts. She died of leukemia on Aug. 29, 1961, at age 15.

That was also near where Elmer Jackson raised cattle for years. On a late winter day in 1953, Jackson was out gathering his herd when there came from the sky "the dirtiest snow he ever saw," according to his son, Norman. There was a burning sensation. He picked up some snow and squeezed. If felt hot.

By the time Elmer Jackson could drive the 35 miles home, he could hardly see, the son said. His face was red and burned. Burns opened on his left ear and the left side of his neck, and they never healed. For the next 19 years, said Norman Jackson, the father continually dressed them with salve.

On Nov. 11, 1968, Elmer Jackson was diagnosed as having thyroid cancer, the son said, and later the family filed a claim for personal injury with the federal government. It was denied. According to the son, doctors said the skin condition was due to exposure to sun, and developed on the left said because Jackson drove south to his ranch in the morning, and north to home at night, and so his left side was more exposed to tanning.

A testing program spokesman said he could remember only one injury confirmed as having been caused by atomic testing. A man was startled by a blast and cut himself while shaving.

The Atomic Energy Commission and its successor agencies long maintained that the nuclear testing program has not been hazardous. Complaints of high leukemia incidents in this area have been investigated briefly by the government and dismissed as not unusually frequent.

"We were guinea pigs," says Irma Thomas, a St. George resident who has tried to get the government to examine its own citizens here as extensively as it has monitored fallout recipients in Japan or Rongelap and on Bikini Island.

And with the Prospect of health investigators returning to this picturesque valley for follow-up study of the 2,000 schoolchildren once checked for thyroid abnormalities, Thomas remembers the time years ago when the government cars pulled up to the high school to examine children.

She remembers the as-yet-unanswered question posed by a school-teacher back then, a question that has since become a mourning cry among many of those who grew up here:

"What have you done to us?"