President-elect Ronald Reagan, in a written response to a question before the November election, said he would work to eliminate a 1962 law requiring drug manufacturers to substantiate claims they make about the effectiveness of their medicines.

He agreed that there is a "clear need for the FDA [Food and Drug Administration] to ensure the safety of drugs," and said the thalidomide tragedy of the 1960s was proof of that.

But Reagan, expressing a view he has held for years but which is rejected by both the industry and his health transition advisory team, went on to say:

". . . The FDA should not be allowed to forbid physicians from prescribing promising new drugs while it engages in seemingly interminable tests to measure . . . effectiveness in all conceivable applications.

"This delay can lead to unnecessary death and suffering. As long as a drug is safe, individuals and their doctors should be free to determine whether its use might be beneficial in their particular cases."

Reagan was replying to one of 16 questions submitted by the Medical Tribune. The weekly, which derives the bulk of its income from prescription-drug advertising and is mailed to physicians free of charge, printed the written exchange Nov. 19. Transition press aides did not respond when asked whether Reagan has changed his stance since the election.

Dr. William W. Walsh, selected by Reagan in May to head his health policy advisory group (HPAG), told The Washington Post last month, "We support the 1962 effectiveness law 100 percent."

A bill to repeal the requirement was introduced in the 96th Congress. The sponsor was Rep. (and now Sen.-elect) Steven D. Symms (R-Idaho). A new repeal attempt, Walsh said, would find "the public . . . up in arms." Repeal critics challenge the broad claim that a potent drug can be regarded as safe if it is ineffective. They say all drugs can cause adverse reactions, and ineffective ones can delay proper treatment while doing no good.

C. Joseph Stetler, former president of the Pharmaceutical Manufacturers Association, said in November interview that the industry would not support "outright repeal of the effectiveness provisions."

Reagan's position accords with statements he made in September 1975 at an American Enterprise Institute roundtable on the purported lag in the introduction here of drugs used in other countries. Rejecting a fellow panelist's suggestion "that my facts weren't verifiable," Reagan said:

"I think something more than 40,000 tuberculars alone have died in this country who conceivably could have been saved by a drug that has been used widely in the last few years throughout Europe."

The drug, rifampin, is highly valued, but there is no way that 40,000 lives could have been lost while it awaited approval here.

Invented in Italy, it went on sale there in 1968. At the end of 1970, Dow Pharmaceuticals and its licensee, Ciba, applied to sell it here, and the FDA approved the application nearly five months later. During that period the number of U.S. tuberculosis deaths -- from all causes, including such major ones as lack of early diagnosis -- was about 1,750.

In a 1976 paper, the American Lung Association said rifampin is but one of four "first-line" TB treatment drugs. The regimen approved by both the ALA and the FDA says it should be used not alone, but with at least one of the other drugs.

Rather than causing TB death rates to plummet, the advent of rifampin contributed to their gradual but irregular decline, as recorded in death certificates: 1970, 5,217; 1971, 4,501; 1972, 4,376; 1973, 1,375; 1974, 3,513; 1973, 3,333; 1976, 3,130; 1977, 2,968; 1978, 2,914. The all-causes TB death total for the nine-year period: 31,327.

The law Reagan wants repealed was so slowly implemented that in 1979 -- 17 years after enactment -- the public paid an estimated $1 billion for prescription drugs of unproved effectiveness.

Of the prescription medicines approved in a recent 27-month period, according to FDA scientists, only 6.4 percent offered "important therapeutic gain," and more than 77 percent represented "little or no" advance over existing products. Of the rest, 14 percent promised "modest" improvement.