At a restricted Air Force bombing range north of Las Vegas, there's a military test site with a mission so sensitive that for years the Pentagon would not admit the place even existed. Built on a barren, chalky lake bed, the secluded air strip is known to military observers as Paradise Ranch or Dreamland because it is believed to have launched the Air Force's most sophisticated cold-war aircraft - from supersonic spy planes to the radar-evading stealth fighter. Although Dreamland's runways, radar stations, and hangars can be seen from a hilltop outside the restricted range near Groom Lake, the site is mysteriously absent from even the most detailed air-defense maps. Signs outside the base warn that photography is prohibited and trespassers are warned that ''use of deadly force [is] authorized.'' But now two lawsuits, filed in federal court in Nevada, threaten to lift the veil of secrecy surrounding this desert installation. The suits allege that the US military used the secrecy cloaking Dreamland's top-flight weaponry to commit and cover up environmental crimes. Four former workers, along with the widows of two others, allege the Air Force burned toxic waste at the site in violation of the 1976 Resource Conservation and Recovery Act (RCRA), Congress's first major toxic-waste management bill. ''The military and its contractors would dig large open pits, then fill the trenches with 55-gallon drums, which were full of paints, solvents, and other chemicals,'' says Jonathan Turley, a law professor at George Washington University in Washington, D.C., who represents the workers. ''The drums would then be covered with jet fuel and lighted with a flare or torch.'' The workers have sued the Department of Defense, the National Security Agency, and the Air Force for allowing the burning to continue. (The suits allege that the burning has taken place, on and off, for the past 10 years.) They have also sued the Environmental Protection Agency (EPA) for failing to inspect and monitor waste disposal at the facility, as required by RCRA. According to the lawsuits, fumes from burning chemicals caused a variety of skin disorders among the workers. Helen Frost's husband was exposed to the chemicals and later died. ''When they go to work up there, they take a nondisclosure oath so they could not talk about work,'' Mrs. Frost says. ''And if they did, they were threatened with Leavenworth [federal prison]. So the first problem was that when we went to the doctor, we couldn't tell him where he, my husband, worked or what what he might have been exposed to.'' Stuck in pretrial dispute But whether or not Mr. Frost, or other workers, became ill as a result of the alleged burning is a question the court is still far from answering. For the last seven months, the litigation has been stuck in a bitter pretrial dispute over whether the trial should be dismissed because information brought out in court might jeopardize national security. To this end, the Air Force has invoked the military and state secrets privilege, a rarely used tenet of common law that allows the executive branch to withhold information if disclosure might jeopardize American soldiers or diplomatic relations. In this case, the Air Force has refused to release even the most basic information about the base: its name, and whether or not jet fuel or car batteries were used at the base, for example. The agency has also asked Federal Judge Phillip Pro to throw both cases out of court. In short, Air Force lawyers argue that because national security precludes the military from divulging any more details, the plaintiffs will not have enough evidence to go to trial. To back this claim, Air Force Secretary Sheila Widnall has submitted two affidavits to the court - one public and one for the judge's eyes only - claiming that any environmental review of the facility entered into the record could educate foreign powers about US military technology. ''Collection of information regarding air, water, and soil is a classic foreign intelligence practice because analysis of these samples can result in the identification of military operations and capabilities,'' writes Secretary Widnall, who entered the fray to meet a key US Supreme Court standard: The secrets privilege must be invoked by the head of the agency seeking protection. So far, the bench is not entirely convinced of Widnall's argument. In a his 30-page opinion, Judge Pro refused to dismiss the complaint against the EPA. Calling the Air Force's arguments ''unpersuasive,'' he ordered its lawyers to hand over all the environmental data on the base by Oct. 2 or get an exemption from President Clinton. Under RCRA, the president may exempt any federal facility from compliance if it is in ''the paramount interests of the United States to do so.'' But because the Air Force did not originally seek that exemption, the plaintiffs' attorney argued that the Air Force invoked its secrecy privileges simply to avoid accountability and stymie his case. The Air Force is not commenting on why it did not seek the exemption, but arguments in court suggest that the agency felt the facility's existence was too sensitive to be brought up even for the public-exemption process. A former National Security Agency staffer himself, Turley contends that most of the chemicals in question are found at any aircraft-production facility. Further, if sensitive data did arise (compounds used in the radar-blunting coat of the stealth fighter, for example) he says it could simply be removed from the public record. Turley hailed Pro's decision as a message that ''national security claims do not trump environmental statutes.'' But because the judge's ruling only affects the workers' complaints against the EPA, it is unclear whether or not the Air Force can still shield key facts about the facility in Turley's case against the Department of Defense. Lawyers for the Air Force, meanwhile, refuse to say whether they will appeal the ruling, seek the presidential exemption, or simply hand over the requested information. Earlier this year, the Air Force signed agreements with the EPA allowing for the first environmental inspections of Dreamland. Pro's decision now overrules the military's insistence that the results of those studies remain hidden. How this case, and Pro's recent decision, will affect future cases involving environmental law and national security is wide open to interpretation, however. Because few environmental lawsuits involve state secrets, most environmental attorneys say the case will not effect the bulk of toxic-waste torts. Chilling effect on whistle-blowers ''This case is yet another chapter in the ongoing saga of trying to force federal facilities to comply with RCRA,'' says Robert Percival, who directs the University of Maryland's environmental law program. ''But I don't expect the government to use the secrecy claim very often in environmental cases. This case is not the tip of the iceberg.'' Still, a successful state secrets claim here could have a chilling effect on whistle-blowers at other sensitive federal facilities, many of which do create extremely toxic byproducts, some experts say. ''To the extent that use of the privilege frustrates this lawsuit, the ability of someone to sue [under RCRA] might be weakened in some cases,'' says Stephen Dycus, a professor at Vermont Law School in South Royalton, Vt., and a leading scholar of environmental and national security law. To others, however, this case is about much more. The Dreamland litigation has become a symbol of what some see as excessive government secrecy in the post cold-war era. ''This is a very important case,'' says Steve Aftergood, who monitors secret weapons programs for the Federation of American Scientists in Washington. Now that the US no longer faces a superpower rival, Mr. Aftergood says, the secrecy surrounding Dreamland is anachronistic, and a ruling for the plaintiffs might force the military to be more candid. While details of the weapons program must be veiled, Aftergood and other critics say that the test site's extreme secrecy created a climate in which domestic law was too easily abused. But to some, these concerns are overblown. Air Force spokesmen will not comment on the case, but they point out that their employer enjoys the cleanest environmental record in the military. Still others add that cold-war level secrecy is still important in the post-Soviet world. ''Just because the Soviet Union is no longer around, that does not mean we don't need secrecy,'' says Kathleen Buck, who served as Pentagon general counsel in the Reagan administration. Balancing the state's need for secrecy against the individual's right to sue is nothing new, however. Ever since Col. Aaron Burr stood trial for treason in 1807, the executive branch has - from time to time - sought to block privileged information from coming out in trials. This privilege was most commonly invoked after World War II, when military and intelligence agencies sought to protect sensitive technology from the Soviets and shroud American eavesdropping practices. In general, the US Supreme Court has allowed the executive branch to use its secrecy powers to block evidence, but not thwart litigation altogether. The Dreamland cases, however, mark the first time the privilege has clashed with environmental law. Because the lawsuits are still in their infancy, it's too early to tell whether or not their outcome will leave a lasting imprint on the legal system, national security, or environmental law, legal experts say.