In a challenge to advertisements for leading pain relievers, including Bayer aspirin and Excedrin, the Federal Trade Commission ruled yesterday that advertising claims about "proven" safety and effectiveness must be backed by clinical tests.

The commission also ruled, in two related decisions, that pain-reliever manufacturers and their advertisers must call an aspirin an aspirin.

The order prohibits Bristol-Myers Co., maker of Bufferin and Excedrin; Sterling Drug Co., which makes Midol and Cope; and advertising agencies Ted Bates & Co. and Young & Rubicam Inc. from indicating that a pain reliever is somehow different from or better than aspirin when aspirin is the chief pain-relieving ingredient in the advertised product.

The main part of yesterday's ruling requires stricter proof for advertising only when it claims evidence that certain products are better than others.

Two advertisements that would require the stricter proof are Bristol-Myers' claim that, "In a major hospital study, two Excedrin work better in relieving pain than twice as many aspirin tablets" and Sterling Drug Inc.'s assertion that "Bayer tested its aspirin for quality, for purity and for freshness against 220 other brands. The tests showed Bayer makes the superior aspirin."

However, the FTC balked at a request by its own counsel to require new advertisements to correct misleading claims in previous ads and narrowed considerably a ruling in a previous case involving Anacin about the types of claims that must be documented or identified in advertising as dubious.

In that earlier case, the FTC decreed that stricter proof was required both for advertising that based claims of superior effectiveness on evidence, and for advertising that made such claims without reference to evidence. Yesterday's ruling imposed the strict standard only in cases where a claim is made that superiority has been "established."

The standard proof required for "established" advertising would amount to two well-controlled clinical tests, the same standard required for both types of claims in the Anacin case.

Among its specific findings, the FTC said that Bristol-Myers falsely claimed that doctors recommend Bufferin more than any other nonprescription pain reliever. It also found that Bristol-Myers, in the case of Excedrin, and Sterling, in the case of Midol and Cope, falsely claimed that the products contained special or unusual ingredients, when--in fact--they contained ingredients commonly used in such products.

Both drug companies said yesterday that they expect to appeal the FTC decision and said that the advertisements questioned in the 10-year-old proceeding are no longer in use.

FTC Commissioner Michael Pertschuk, who with commissioner Patricia P. Bailey objected to narrowing the requirement of substantiation, said that the decision may leave unsolved the "central problem" that the FTC hoped to settle with its pain-reliever cases--the profusion of mutually inconsistent claims by analgesic makers that each produces the most effective pain reliever."

Brand-name pain relievers, backed by millions of dollars in advertising, typically cost two or three times more than plain aspirin.

Bristol-Myers general counsel, J. Richard Edmondson, called the FTC decision "erroneous as a matter of law and contrary to the evidence presented."

Sterling said yesterday that it was "pleased that the FTC did not find false or misleading Bayer aspirin's advertising claims of overall pharmaceutical superiority over other aspirin." While the FTC did not question the claim of "pharmaceutical" superiority, which deals with manufacturing quality, it criticized the claim, saying consumers could be confused into thinking the product was more effective.

Dr. Sidney Wolfe, director of the Public Citizens Health Research group, was sharply critical of the decision, which he said would require less substantiation of misleading claims. Wolfe also challenged the commission's decision not to seek corrective advertising.

"Once people become convinced by false and misleading advertising, they need something more. They need the jolt of a corrective ad." Wolfe said that advertising similar to the advertisements reviewed in the FTC decision is still in common use.