Eighteen major American companies have tested the genes of workers for genetic defects or damage, and 59 companies say they are considering using the tests, according to a congressional report released yesterday.

Such testing could save lives by warning workers of hazards, but also has "a dark Orwellian underside" and a potential for "wholesale discrimination" against workers, said Rep. Albert Gore (D-Tenn.), one of the congressmen who requested the study by the Office of Technology Assessment.

The tests are not yet considered accurate enough to be scientifically valid, but may in the future be used in two ways: to determine whether genetic damage is being done to workers by hazardous chemicals or radiation, and to determine whether some workers are more susceptible to disease than others because of their genetic makeup.

Until now, tests have apparently been conducted only for research purposes or, in the case of sickle cell trait, at the request of employes.

The government estimates that at least 10 million American workers are exposed to hazardous chemicals or radiation regularly. "It is clear that because of the high stakes, this technology will soon be used much more widely... and if the tests are validated the legal pressures will be so great as to ensure their rapid spread," Gore said. He suggested establishing guidelines now, before the tests proliferate.

The OTA report contains the first major survey of American companies on genetic testing. The survey asked officials of the Fortune 500 companies, 50 of the nation's largest utilities and 11 unions whether they have used genetic testing, are using it now, or may possibly use it in the next five years. The OTA received 366 responses.

Geoffrey Karny, director of the project for the OTA, said among the most significant numbers in the survey are those that show 59 major companies possibly using genetic testing in the next five years.

Only a few genetics traits have been identified that might in theory make workers more vulnerable to hazardous agents. One of them is the sickle cell trait, which is a normally harmless defect. It has been suggested that the presence of hazardous chemicals that affect blood production may put workers with sickle cell trait at greater risk than other workers.

One of the special hazards of genetic testing is that traits often occur at different rates in different groups, so discrimination on the basis of genetic traits can also amount to discrimination on the basis of race or sex.

Gore laid out two hypothetical cases to illustrate the dilemma raised by genetic testing. In one case an applicant for a job in a cotton mill has a 5 percent higher susceptibility to the occupational disease called brown lung. Can he be rejected? In another case, a hemophiliac, whose disease causes uncontrollable bleeding even from very small cuts, applies for a job as a butcher. Should he be rejected?

When asked where to draw the line in such cases, Gore said, "The legal and ethical establishment responds with a collective shrug of the shoulders." Gore said he has asked two federal agencies to draw up guidelines to assure that the tests would be scientifically valid and would not be used to discriminate against groups of workers.

He said he asked the National Institute of Occupational Safety and Health to set guidelines on what makes a valid test, and asked the Equal Employment Opporunity Commission to study how genetic tests should be used in making employment decisions.