Nuclear testing no longer supports boom town : The Cold War’s demise has imperiled the future of a desert enclave near atomic bombing site.

When you turn off U.S. Highway 95 on the five-mile-long spur road that takes you to Mercury, you pass two square compounds surrounded by high chain-link fences.

They are holding areas, one for men and one for women. For years, peace demonstrators who periodically blocked the road into Mercury and the U.S. nuclear weapons test site were detained in the rocky, unsheltered pens. Afterward, buses hauled them away to be booked on formal charges.

Now, the pens are little more than relics of the Cold War.

And Mercury itself may not have much of a future.

More than a town, this desert enclave was and is a base camp for the sprawling desert test site where the United States exploded 925 atomic bombs between 1951 and 1992. But a year and a half has passed since the last “shot” in the Nevada desert. Whether there will ever be another one is an open question.

Test workers are already being laid off. Total employment for the entire weapons-testing program is down to 7,000 from a peak of 10,000. As many as 500 more jobs may be lost at the 1,350-square-mile test site before the year is over.

Workers who remain pore over the results of the most recent underground explosions and maintain two sites where preparations for tests were almost complete when President George Bush declared a moratorium in 1992. President Clinton has extended the ban through September, 1994, provided no other countries resume testing.

Mercury can be excused if its feelings are ambivalent.

Time was when its dormitories were filled to capacity, and communities of campers, trailers and mobile homes were crowded. At one time, more than 6,000 soldiers camped in tents at Camp Desert Rock, a temporary post just to the south.

The movie theater and the bowling alley were booming in those days, as was the post office, the cafeteria, the laundry and all the offices and warehouses clustered in the valley. Scientists from Los Alamos and Lawrence-Livermore Laboratory regularly flew in and out of Desert Rock Airport, along with government officials from Washington and cargo planes bringing explosives to be tested.

In the days when tests were still conducted in the atmosphere--bombs dropped from planes, suspended beneath balloons or mounted in high towers--reporters from around the world were ushered through. Out on a pile of rocks called News Nob, they could watch mushroom clouds rise into the stratosphere. They made Frenchman Flat and Yucca Flat internationally known datelines during the strategic arms race.

Above ground and underground, the explosions during four decades left the desert floor so pockmarked by craters that high-altitude photographs of the area looked more like the moon than the Earth.

The largest atmospheric test, called Hood, created a 74-kiloton explosion in 1957. The largest underground shot was 1.3 megatons, 65 times the power of the bomb that leveled Hiroshima in 1945.

There were other memorable explosions as well. Not long after the site opened in 1951, a device dropped from a B-50 bomber above Frenchman Flat broke store windows in Las Vegas. Sedan, a 104-kiloton device exploded 635 feet underground, lifted 12 million tons of earth into the sky. Part of a program to demonstrate the utility of nuclear explosives in earth-moving projects, it created a crater 1,250 feet in diameter and 320 feet deep.

With worldwide concern over radioactive materials entering the food chain, atmospheric tests were banned by the Limited Nuclear Test Ban Treaty negotiated in 1963. Its restrictions have since been stiffened. In 1990, the United States ratified another treaty, negotiated during the Richard Nixon Administration, that limited the size of underground tests to no more than 150 kilotons.

Throughout the history of the test site, the government was able to conduct smaller explosions deep underground that went undetected for decades. Last year, in keeping with its new policy of openness, the Energy Department recently announced 204 tests never before acknowledged.

These days, however, the only activity on the test site is the arrival of visitors to tour the craters and see the ghostly remains of the bridges and buildings that were erected in the desert to help experts study the effects of nuclear weapons.

They can look into the giant Sedan crater, where Apollo 14 astronauts later trained for their visit to the moon. They can drive into the Bixby crater, created by a blast that sent memorable tremors through Las Vegas. They can visit the site of the Apple II test, where a house was seared but Joshua trees, 200 years old and more, survived.

And they can still find the trenches, now overgrown by scrub, where soldiers crouched, getting as close as troops have ever come to combat on a nuclear battlefield.