LAS VEGAS — Alma Mosley sits alone in her cluttered house and thinks about justice.

Fallen behind a chest of drawers, unreachable, is a framed certificate for work well done, illustrated with a mushroom cloud and inscribed with her husband's name: Hugh Mosley. He has been dead since 1978, lost to colon cancer--a victim, she says, of the Nevada Test Site, where he labored for 13 years at the height of the nation's nuclear weapons testing program.

But a federal judge here has disagreed, ruling there was not enough evidence to conclude that radiation caused the illnesses of Hugh Mosley and five other men who worked at the site in the harsh Nevada desert long ago. The judge said that for some of the men, lifestyles--diet or cigarettes or alcohol--may have been to blame.

"My husband was a \o7 clean \f7 man," says the diminutive Mosley, voice charged with pain, spine stiff with indignation. "He neither drank nor smoked. It was a slap in the face. . . . There's no justice in this government. They killed my husband, my children's father, and said they didn't."

The workers case, as Mosley's was called, was the last big Nevada Test Site radiation lawsuit against the government to finish trial.

This stretch of desert--a restricted swath of sand and sagebrush larger than Rhode Island, pocked with craters from nuclear blasts and shrouded with the secrecy of its Cold War past--was the site of more nuclear warhead detonations by the U.S. government than any other place in the world.

More lawsuits have been focused on this location, 65 miles northwest of Las Vegas, than on any other stop along the so-called Atomic Trail--the nuclear weapon's path from uranium mine through manufacturing plant to proving ground. More protesters have been arrested here than at any other target of anti-nuclear activity in the country--including more than 1,200 on one day alone in 1988.

But with the workers case possibly at an end--an appeal is uncertain--and U.S. nuclear testing halted for at least the next 14 months, a notorious chapter in the nation's weapons history may be coming to a close. As the United States heads toward next year's 50th anniversary of the bombing of Hiroshima and Nagasaki, the Nevada Test Site is on the precipice of a dramatic change:

* The world's nuclear powers began meeting again last week in Geneva to continue work on a comprehensive nuclear test ban treaty that could render the Nevada site unnecessary.