In the still air of this desert valley, home to the world's largest stockpile of chemical weapons, a collective sigh of relief is almost audible.

In nearly two years of operation, a prototype chemical weapons incinerator has destroyed 1,500 tons of sarin gas, one quarter of the depot's stock. Zeroing in on faulty lots of weapons, disposal workers also cut the number of "leakers" last year to 27, two-thirds the annual average number of bombs found to be leaking chemical gas here in the 1990s.The results - and the local revenue - have prompted at least one local official to suggest transporting other chemical weapon stocks to here for destruction, although the idea is widely opposed.

Environmentalists had bitterly fought the Tooele incinerator, once predicting that workers would come out in "body bags." But the only recorded injuries have been to two workers who slipped on icy walkways outside the incinerator, 17 miles south of Tooele (pronounced too-ELL-ah), a booming bedroom community of about 15,000 people in north-central Utah.

"My constituents are pleased we are finally getting rid of this stuff," said the local official, Gary Griffith of the Tooele County Commission, which has long supported the incineration of the weapons here.

The massive incinerator is the world's most concrete advance in weapons reduction since the Chemical Weapons Convention went into effect one year ago. This treaty rules out the methods of disposal that were popular through the 1970s: open burning on windless days, burial by bulldozers and dumping in the ocean.

Tooele's incinerator, which resembles a steamship beached in the desert 45 miles southwest of Salt Lake City, is the fruit of 20 years and several billion federal dollars in research and construction.

"This is the Rolls-Royce of incinerators," said Amy Smithson, who has reviewed the plant's operation and who is a senior associate at the Henry L. Stimson Center, a research organization in Washington that specializes in military issues. "The Army has put more safeguards on this incinerator than exist on any incinerator in the world."

Russian technicians have toured the Tooele incinerator as part of efforts to destroy all of their country's stocks. But Russia, whose 40,000 tons of chemical weapons is the world's largest stockpile, is not expected to meet the treaty's 2007 deadline, because its government lacks sufficient money.

In the 1980s, the U.S. military withdrew all its chemical weapons stocks from Europe and shipped them to Johnston Atoll, in the Pacific. An incinerator started operating there in 1993 and has burned about 1,500 tons, or almost 75 percent of the stocks.

Two more chemical weapons incinerators are under construction at storage sites in the United States: one at Anniston, Ala., the other at Hermiston, Ore. A construction contract is to be awarded soon for an incinerator at Pine Bluff, Ark. And government researchers are testing chemical neutralization technologies for possible use at the other stockpile bases: Aberdeen, Md; Richmond, Ky; Newport, Ind.; and Pueblo, Colo.

But environmentalists continue to try to block all incinerators, including Tooele's, saying they are unsafe.

"Our lawsuits are meant to derail the technology, not to derail the U.S. mission," said Craig Williams of the Chemical Weapons Working Group, a citizens coalition based in Kentucky. "These facilities, as they are designed and operating, do not protect the public."

Utah has reason to be skeptical about the military's safety claims. In Nevada in the 1950s, the military exploded nuclear bombs in open-air tests when the wind was blowing away from Las Vegas and toward Utah. In 1968, about 6,400 sheep were accidentally killed when the wind changed during an open air test of a nerve agent at the Dugway Proving Ground, an Army installation about 40 miles west of here.

But a series of scientific reviews seems to be easing public fears about Tooele's incinerator, the first to operate in the continental United States. In two telephone surveys conducted last year by Dan Jones and Associates, a polling group, the number of respondents in the Salt Lake area who considered the incinerator risk to be "significant" or "very significant" dropped sharply, to 28 percent in September, from 44 percent the previous March.

Last year, a panel of 16 independent scientists reviewed operations at the Tooele plant at the request of the National Research Council. In its report, the panel upheld Army calculations that said burning Tooele's munitions would be far less dangerous than storing them.

Then in September, a separate study rated "prospects for continued safe operation" of the incinerator as "very good." This report was prepared by independent consultants contracted by the Utah Citizens Advisory Commission, a diverse group appointed by the governor, Mike Leavitt, a Republican.

The report was commissioned after a series of plant shutdowns and accusations of lax safety practices by former managers at the Tooele Chemical Agent Disposal Facility, as the plant is officially known.

"While there have been highly publicized problems and occurrences at T.O.C.D.F.," the report said, "these have been very minor with respect to both public and worker safety. None of these have resulted in release of measurable amounts of agent into the atmosphere, and no appreciable agent exposures have occurred to workers, visitors or the public."

In a highly computerized plant dependent on robots, shutdowns are to be expected at the outset, the report said. But the reported added, "The operating staff are gaining experience, and operations are becoming more routine."

Oversight is so heavy, the report said, that some managers spend up to 50 percent of their time responding to inspections and audits. In a 10-month period, there were 28 outside evaluations of the incinerator.

Next June, a permit to double the plant's rate for incineration is expected to be issued by Utah's governing agency, the Solid and Hazardous Waste Control Board.

So far, the incinerator has destroyed almost 14,000 rockets, bombs and bulk containers in the process of burning the sarin gas. With the perception of a smooth operation, some people here have been emboldened to challenge inhibitions on transporting chemical weapons.

Government plans to duplicate Tooele's $650 million disposal plant at the seven other sites around the nation represent a colossal waste of taxpayers' money, argues Griffith, the county commissioner.

"None of this stuff was hatched here to begin with," he said of the chemical weapons that were shipped here by rail and road, largely from a Denver production plant, in the 1950s and 1960s.

Arguing that stocks in Colorado, Arkansas and Oregon should be shipped to Tooele for incineration, Griffith said duplication meant that "we are spending billions for nothing."

"We let mass hysteria, lack of common sense, steal money out of our pockets," he added.

But on a broader state and national level, his idea does not have much support. And locally, some environmentalists say they suspect county officials are falling in love with their plant for economic reasons. Under the conditions for incineration, the county receives $970 from the Army for every ton of chemical agent incinerated. These royalties, about $1.5 million so far, are helping to finance the construction of a sports complex on the edge of town.

Before the incineration began at the Tooele incinerator on Aug. 22, 1996, the Desert Chemical Depot, as the Army installation is officially known, held 13,600 tons of chemical weapons, or 43 percent of the nation's total arsenal of 31,500 tons.