For years, reporters and anti-nuclear activists heard rumors that the government may have tested atomic bombs in the 1950s at Utah's Dugway Proving Ground.

Now, once-classified documents obtained by the Deseret News may show why such apparently false rumors spread.The documents reveal that nuclear scientists unleashed large, secret underground explosions at Dugway in May 1951 - and maybe at other times - with non-atomic conventional weapons to study effects expected from future underground atomic blasts in Nevada.

The blasts occurred about the same time Dugway was conducting separate, smaller explosions to spread radioactive materials through the wind to see if that could contaminate battlefield areas - which was secret until a year ago.

In short, discussions of huge explosions conducted by the military's nuclear weapons experts, plus talk of other tests spreading radioactive dust, likely caused rumors of atomic blasts in Utah.

"We had been told by some people that the government exploded an atomic bomb at Dugway in the spring or summer of 1951," said Preston J. Truman, president of the Downwinders watchdog group.

That's when the other tests occurred. Truman said various people have also reported possible atomic blasts at Dugway in May 1952 and in 1954. "We always questioned those reports. It seems more people would have noticed," Truman said.

The Army says the rumors are false.

"I have reviewed numerous historical records at Dugway Proving Ground and have not discovered any records of above-ground or underground nuclear testing conducted at DPG," Dugway radiation protection officer Clair D. McBride wrote in response to a Deseret News Freedom of Information Act request.

He added, "I do not know of any individual (who) remembers any such testing at DPG, and I have not observed any physical evidence (i.e. large craters, no vegetation) of such testing."

Moreover, the official Energy Department list of atomic and nuclear bomb tests does not include any at Dugway. It says tests occurred in Nevada; Alamogordo, Farmington and Carlsbad, N.M.; Hattiesburg, Miss.; Grand Valley and Rifle, Colo.; Amchitka, Alaska; and islands in the Pacific Ocean.

The issue of possible Utah atomic tests came up again last month when President Clinton's Advisory Committee on Human Radiation Experiments released some documents that seemed to suggest - but were unclear about - possible atomic work at Dugway.

Minutes of a committee that in May 1951 was looking at the safety of planned Nevada "ground-bursts" of atomic weapons - which create more radioactive fallout dust than bursts high in the air - refer to tests then being conducted at Dugway.

A member, W. Bleakney, is quoted as saying, "We had a hand in planning some of the original tests at Dugway, but they were discontinued after the first year, and I have not been in touch with that since it was started again."

Later, A. Spilhaus of the Armed Forces Special Weapons Project, which oversaw development of nuclear weapons, also mentioned Dugway tests when asked if explosives alone could provide data about fallout and craters of atomic ground-bursts.

Spilhaus said, "This is being done now at Dugway. The largest one is 320,000 pounds - that is being fired tomorrow, by the way - and this is in very similar soft and sandy soil" compared to the soil at the Nevada Test Site.

In response to a Deseret News Freedom of Information Act request, Dugway released a once-classified document it found about that test on May 22, 1951.

The Armed Forces Special Weapons Project, the military's nuclear weapons experts, ignited conventional explosives with the impact of 320,000 pounds of TNT (or 0.16 kiloton) that were buried 35 feet underground at Dugway's White Sage Flats.

The smallest of the atomic and nuclear blasts at the Nevada Test Site had similar yields, but most were much larger.

The document notes that smaller explosions at Dugway occurred earlier that month as part of the same experiment, 40,000 pounds of TNT on May 10 and 2,560 pounds on May 5.

It said other tests of similar magnitudes were to be conducted in solid rock and in other types of soils.

Documents say the tests were primarily to help "in the prediction of the detailed effects of nuclear explosions" on both above-ground and underground structures (such as tunnels) from underground nuclear tests.

The document reported results only for above-surface test structures built at Dugway from the blasts' ground motion, dust "throwout" and air blast. It was designed to help build safe structures at the Nevada Test Site.

It noted the large blast "produced permanent deformation" of most nearby test structures, and caused several to collapse.

On May 29, 1951, only a week after the large conventional explosion, Dugway - in a separate series of experiments - exploded four different shapes of radioactive munitions on 50-foot poles to see which would best spread contamination, according to previously released reports.

Documents obtained by the Deseret News and government investigators over the past year have shown at least 74 tests at Dugway spread radioactive dust and pellets to the wind between 1949 and 1953.

The non-atomic tests scattered radioactive dust to determine if battlefield areas could be contaminated with them during wartime. Documents say the total amount of radiation released by those tests was 153,000 curies - or 10,000 times the 15 curies released by the near-meltdown at the Three Mile Island nuclear plant.

Army and Energy Department studies say, however, that radioactive material used, tantalum-182, had a short half-life, and therefore any remaining traces at Dugway have long since ceased to be dangerously radioactive.