The Supreme Court has been asked to decide whether a cost-benefit test must be met by federal rules intended to assure safe and heathful conditions for millions of workers exposed to cancer-causing substances.

Although the case directly involves only benzene, the 12th most widely used industrial chemical, the Labor Department says that its ability to regulate other carcinogens in the workplace may well be at stake. The department's adversaries, including the oil, chemical, rubber and steel industries, disagree.

The department's Occupational Safety and Health Administration has survived challenges to the standards it set for exposure to three other carcinogens, asbestos dust, vinyl chloride and coke-oven emissions, in the U.S. Courts of Appeals for the District of Columbia and the 2nd and 3rd Circuits, respectively.

In the case of benzene, however, the 5th U.S. Circuit Court of Appeals last October set aside the OSHA standard, saying that it "will not attempt to reconcile" its decision with the others.

The court agreed with Labor Secretary Ray Marshall that substantial evidence supports his finding that benzene causes cancer as well as other diseases, some of which are fatal, and that the permissible exposure level under the standard -- one part per million during an eight-hour workday -- poses a lesser risk than the previous 10 ppm level.

The opinion for the court also recognized the current impossibility of determining an exact relationship between decreased exposure and decreased risk. And it didn't dispute that one ppm is a feasible standard, economically as well as technologically, or that the law creating OSHA calls for the "highest degree" of protection.

But, Circuit Judge Charles Clark wrote, the law doesn't give the secretary "unbridled discretion to adopt standards to create absolutely riskfree workplaces regardless of cost." Rather, the law requires "feasible standards" based on "the best available evidence," he held.

"Until OSHA can provide substantial evidence that the benefits to be achieved by reducing the permissible exposure limits from 10 ppm to one ppm bear a reasonable relationship to the costs imposed by the reduction, it cannot show that the standard is reasonably necessary to provide safe or healthful workplaces," Clark wrote.

"OSHA's failure to provide an estimate of expected benefits for reducing the permissible exposure limit, supported by substantial evidence, makes it impossible to assess the reasonableness of the expected costs and benefits," Clark said. "This failure means that the required support is lacking to show reasonable necessity for the standard."

In separate petitions for an expedited review -- and for a decision by the end of the current term in June or July -- Solicitor General Wade H. McCree Jr. and the AFL-CIO's Industrial Union Department both argued that Clark had misread the intent of Congress and the actual language of the law, as interpreted by the three other appeals courts.

"The decisions do not simply conflict in result," McCree said in behalf of the Labor Department. "They imply completely different reasoning." Citing expert testimony that there is no known safe level of exposure to a carcinogen, McCree said:

"The three earlier decisions recognized the authority of the secretary... to resolve doubts in favor of safety. They do not require [him] to establish the 'savings' attributable to a reduction in exposure; the decision in the present case makes such a computation essential."

The IUD petition said that the ruling also threatens standards Marshall has set for three other carcinogens, inorganic arsenic, cotton dust and lead, after he was unable to determine the exact effect of low-level exposures.

Each of these standards is currently being challenged in federal appeals courts, including the 5th Circuit. In addition, a challenge to the 3rd Circuit ruling in the coke-oven emissions case is before the high court.

"Moreover, the standards presently under review are only the first... that must be set to regulate the myriad of carcinogens in the workplace," the IUD said. If the Supreme Court doesn't resolve the question of the secretary's power to issue standards for carcinogens, he "will be unable to get on with the congressionally mandated job of protecting American workers," the petition said.

By contrast, trade associations for the petroleum, chemical and rubber industries urge the court to leave the 5th Circuit ruling standing, terming it "perfectly sensible," not in conflict with the holdings of other circuits, and no threat to the proper regulation of benzene or other toxic substances.

The associations, along with the American Iron and Steel Institute and other groups and companies, contend that the evidence on benzene didn't justify the strict new standard.

Benzene is used mostly as an ingredient of other organic chemicals and partly in the production of gasoline, detergents, pesticides, solvents and paint removers.

The Labor Department adopted the 10 ppm benzene standard in 1971 to protect workers -- now estimated to number 629,000 at 150,000 work sites -- from nonmalignant diseases.

Later, the National Institute of Occupational Safety and Health warned that benzene also might cause leukemia. In May 1977, after a public hearing, Marshall issued the tighter one ppm standard. He rejected as unpersuasive several industry-cited studies purporting to show that workers exposed to benzene didn't develop the blood cancer, saying that the studies hadn't separated exposed from unexposed workers.

Concluding that there was no known safe level of exposure, Marshall ruled that one ppm complied with the law's requirement for a standard that "most adequately assures, to the extent feasible," that "no" employe's health be impaired in the workplace.

He acknowledged that he could not pinpoint the benefits of reducing the permissible exposure to one ppm, but said that it was "the lowest feasible level" and would save lives and thus achieve "appreciable" health benefits.

At the same time, Marshall said, he could estimate the cost: An investment in engineering controls of $266 million, and anuual outlays of $187 million to $205 million in the first year and $34 million thereafter.

In the asbestos-dust case, the appeals court here explicitly rejected the proposition that the law requires -- or even permits -- the secretary to act on the basis of a cost-benefit comparison.