Food and Drug Administration scientists have judged that only 6.4 per cent of the prescription medicines the agency approved for sale in a recent 27-month period offer "important therapeutic gain," while more than 77 percent offer "little or no" advance over existing products. Of the balance, 14 percent promise an improvement rated as "modest."

The FDA's Bureau of Drugs made the evaluations, which are in a document obtained under the Freedom of Information Act by the Health Research Group. The HRG, which is financed by Ralph Nader's Public Citizen In., released it to the press yesterday.

The scientists evaluated the 171 medicines that the FDA approved for sale between October 1975 and January 1978. Under current drug law, a new medicine simply must live up to the claims made for it. Nothing in the law requires it to be better than, or even as good as, drug already being sold.

The document is one of three on the therapeutic significance and human testing of new drugs cited by the HRG in a letter to FDA Commissioner Donald Kenneday.

A Second paper shows that of the experimental drugs that graduate from animal to human testing, less than 1 percent offer important therapeutic improvement, the HRG said.

This paper, "Research From Washington: Health Care," was issued in September by Smith Barney Harris Upham and Co. Inc., a Wall Street securities firm that reports to clients on drug stocks, and the HRG said, derives from FDA data.

"In other words, a large number of drugs are being tested in humans, whose health and lives are put at risk without any benefit to themselves or society," said Dr. Sidney M. Wolfe, HRG's director, and Ben Gordon, and associate and former Senate subcommittee economist.

Both papers bear on charges that American have been hurt by a "drug lag" - a slowdown in the number of new drugs introduced in the United States as compared with other countries that do not require manufacturers too prove drugs to be both safe and effective.

Some critics, including Nobel laureate economist Milton Friedman have long cited the purported lag in urging repeal of the requirement to prove efficacy. Friedman has advocated abolition of the FDA.

The materials released by the HRG reinforce the conclusion reached last May, after a two-year study, by a special outside panel on drug regulation created by the Department of Health, Education, and Welfare.

The efficacy requirement isn't to blame for the claimed lag, the panel said. It termed "unclear" whether some new drugs sold abroad are truly significant advances over those sold here, adding,"Moreover, insufficient weight appears to have been given to adverse reactions and drugs which are marketed abroad [but] are not available here."

In addition to Friedman, two of the most publicized critics of the claimed lag have been University of Rochester School of Medicine physicians and pharmacologists, Drs. Louis Lasagna and William Wardell.

But in the third paper, a study for the National Science Foundation (NSF) Lasagna and Wardell say that drug regulation has not appreciably changed the number of drugs that offer important therapeutic gains, Wolfe and Gordon disclosed.

The number of people receiving experimental drugs at any one time is about 250,000, according to a July 1976 estimate by the General Accounting Office, the auditing arm of Congress.

If all these drugs were withheld from humans until animal tests establish whether they cause cancer or have other long-term effects. 43.5 percent of the drugs never would be given, Lasagna and Wardell estimate in their paper for the NSF, "Technological Innovation and Government Regulation of Pharmaceuticals in the U.S. and Great Britain."

As translated by Wolfe and Gordon, these means that "over 100,000 of these human experimental subjects would be spared exposure to dangerous drugs - most of which have little or no therapeutic values - if animal tests were done before humans were exposed rather than after."

They charged that pharmaceutical industry research and development, do not focus "on major advances in therapy for consumers." In this regard, they cite this assessment in the Smith Barney client memo: ". . . it is entirely possible that the economic winners would come from drugs which the FDA estimates to be either of moderate or 'little or no' therapeutic gain."

Wolfe and Gordon urged Commissioner Kennedy to implement a 1972 HRG petition to require animal studies to be completed before human studies are started, and to ask Congress to change the drug law to allow on the market only those new drugs that are safer and more effective than old ones.