At least 10 percent of major American companies might begin genetic screening of their current and prospective employes to determine susceptibility to work-related diseases--data that could be used in hiring and firing, according to a congressional study released yesterday.

Information from genetic testing, usually blood tests, might be used not only as a basis for personnel decisions, but also to collect research data and serve as an early warning system of hazardous conditions.

Only six of the 366 companies that responded said they currently conduct genetic testing of employes. But 59 companies, or 16 percent of those responding, said they were considering conducting genetic screening within the next five years. The study surveyed the companies in the Fortune 500 and the 50 largest U.S. utilities.

Rep. Albert Gore Jr. (D-Tenn.), who chaired a House subcommittee hearing on the issue, said the companies' unexpectedly high interest in genetic screening signaled the need for congressional action to make certain the data collected from such tests are not misused.

"If we learn to predict which individuals are more likely to be harmed by exposure to certain substances, it has potential to serve as a marvelous tool to protect the health of workers, or as a terrible vehicle for invidious discrimination," Gore said at a hearing on genetic screening in the workplace by a House Committee on Science and Technology subcommittee.

Gore warned that genetic testing is now at the level of a "black art" with uncertain reliability in predicting which workers are more vulnerable.

"Nevertheless," he said, "companies are rushing headlong into this technique" because they fear lawsuits by workers who develop the diseases and claim the companies should have screened them to determine they were at a higher risk than fellow employes.

The use of the tests is especially controversial because various traits uncovered by genetic screening--sickle cell anemia trait in blacks, for instance--are often linked to a particular race, ethnic group or sex. Critics fear that genetic screening could, in effect, result in discrimination against workers who are members of such groups, even though federal law bars companies from directly practicing such discrimination.

"It is currently considered irrational and wrong to exclude workers as a result of black skin or because they are male or female, but if one has a genetic makeup making one 10 percent more susceptible to disease, does that justify excluding?" Gore asked. "At what point is it invidious discrimination to deny a person a job on the basis of genetic heritage?"

Critics are also concerned that companies will use genetic screening as a tool to avoid keeping their workplaces as safe as possible, hiring only those workers who are not susceptible to disease.

Dr. Kenneth Miller, medical director of the Workers Institute for Safety and Health, said companies should not be allowed to cut corners on safety as a result of genetic screening. A risk to susceptible workers "is a risk to everyone," although "maybe some will get their cancer sooner than others," Miller said.

More companies might have responded to the survey, Gore noted, if an industry trade group given a confidential final draft of the questionnaire had not circulated copies to its members with critical comments and a warning that the anonymous questionnaires appeared to contain identifying marks.