The Carter administration has decided to continue the practice of authorizing drug companies to use prisoners as human guinea pigs. The United States is the only nation that still officially approves of such experiments, including behavior control and the testing of potentially lethal drugs and vaccines on a prison population.

Some reformers had hoped that the Department of Health, Education and Welfare would at least dramatically tighten controls on drug testing, in line with recommendations of an influential national commission that looked into the issue last year. But the new regulations, which have just been cleared through the department and are awaiting HEW Secretary Joseph A. Califano Jr.'s signature, are understood to fall short of the commission's recommendations.

They will not insist - as the commission had proposed - that drug companies show compelling reasons for using a captive population for their testing. A high-level source at HEW said yesterday that the department thought there were legal complications to applying such a demand on drug companies.

The recent revelation about the Central Intelligence Agency's past use of mind control and drug tests on American citizens has focused new attention on the issue of human guinea pigs. The use of prisoners by U.S. drug companies and federal agencies, including the Public Health Service and the Army, has not, at least in recent years, involved such extreme attemtps at brainwashing, creating amnesia and changing personalities. Nor has it involved people without their knowledge, as some of the CIA test did.

Nevertheless, many opponents of drug testing on prisoners have maintained that the concept of informed consent is impossible to apply in a prison. Yet the American drug industry tries out roughly 85 per cent of its new drugs on inmates. Some drug companies have been allowed to operate their facilities inside prisons to take advantage of the prison population.

Last year, the National Commission for the Protection of Human Subjects of Blomedical and Behavioral Research conducted a lengthy study for HEW and concluded that the United States was the only country that allowed such tests on prisoners.

It found that, as an extra inducement, companies sometimes paid 10 times as much to prisoners to become human guinea pigs as they could earn in other prison activities. Usually this was still more convenient and profitable for the companies than going to outside volunteers.

Although nearly all the prisoners interviewed by the commission approved of the experiments, it concluded that prison conditions did not provide "a sufficiently high degree of voluntariness and openness." It found "strong evidence of poor conditions generally prevailing in prisons and a paucity of evidence of any necessity to conduct research in prisons."

The Bureau of Prisons last year decided to call a temporary halt to all biomedical experimentation on prisoners unless it was directly intended to improve prisoners' health. This move still left the state and county jails, where in 1975, according to the Pharmaceutical Manufacturers Association, at least 2,400 prisoners were used, often repeatedly.

In spite of its findings, the commission decided that prisoners could continue to be used as human guinea pigs in tests that would have no direct benefit to their health. But it laid down new conditions.

Payment should be increased so that it was as high as that offered to outside volunteers.

A high degree of voluntariness should be ensured by making it clear that there was no link between a prisoner's participation in the experiments and his chances for parole by improving living conditions, by giving prisoners an effect system or redress for grievances and by opening the test program to public scrutiny, including the rights of prisoners to write uncensored letters."

The onus of proof should be on the drug companies to show that their experiments fulfilled "an important social scientific need" and that the reasons for using prisoners rather than other people were "compelling."

The 11-member commission decided that although prisoners might say they took part willingly in experiments respect for their humanity demanded that they be protected against forces that appeared to dictate their choice.

Dr. Donald Shalkley, an HEW spokesman, said the department had concluded that it was impossible under the law to define what was an important social and scientific need and what reasons were "compelling," and that the department could not promulgate regulations based on unclear definitions. Only where the research was directly subsidized or supported by the federal government could such tight restrictions be imposed, it concluded.

Dr. Roy Branson, a senior research scholar at the Kennedy Institute's Center for Bio-ethics at Georgetown University who gave evidence to the commission, has warned that failure to demand compelling reasons from the drug companies "will be a major step backwards in the country's attempt to protect prisoners from exploitation."

There are fears that the drug companies will bring pressure on the federal government and the eight states that have stopped tests on prisoners to reverse their policy.