The Bristol-Myers Co. suffered Excedrin headache No. 1 yesterday, courtesy of the Federal Trade Commission.

An FTC administrative law judge ruled that advertising claims that Bufferin, Excedrin and Excedrin p.m. are safer of more effective than aspirin have not been scientifically proven, and ordered Bristol-Myers to say so, in any future ads that have such claims.

The law judge's decision is subject to approval by the FTC, which has five members.

The company immediatly branded the judge's findings "erroneous . . . and contrary to the evidence presented," asserting that all three affected products "have been used for many years by millions of satisfied customers.

Nevertheless Judge Montgomery K. Hyun ordered Bristol-Meyers to qualify its claims. It would have to say, for example, that "Bufferin has not been proven to be gentler to the stomach than aspirin," or "Excedrin has not been proven to be a stronger pain reliever than aspirin." As an alternative, it could simply stop making the gentleness and strength comparisons.

The judge also barred the company, and the two New York advertising agencies which developed the advertsements in question, from representing, without a reasonable basis, that the three products are good for tensions, nervousness or stress.

"The record clearly shows that Bufferin, Excedrin and Excedrin p.m. will not relieve tension." Hyun said.

Hyun specifically criticized Bristol-Myers claims that Bufferin worked faster than other products. "It has not been siginificantly established that the speed of relief provided by Bufferin is significantly greater than that provided by plain aspirin," Hyun said.

Hyun ordered Bristol-Myers and Ted Bates & Co., one of the two advertising agencies, not to make unsubstantiated claims that physicians recommend Bufferin more than any other nonprescription pain reliever.

Hyun cited studies done for the FTC which found that doctors recommend a nonaspirin pain reliever and generic aspirin more often than Bufferin.

He ordered the two companies and Young & Rubicam Inc., the second advertising agency, to disclose that all three products contain aspirin to help consumers make a choice, and because of adverse side-effects aspirin can have on some people. Brisol-Myers had used the worlds "analgesic ingredient" to describe aspirin. Young & Rubicam handled the Excedrin account.

"The record shows that a substantial number of consumers do not know that the analgesic ingredient is aspirin," Hyun said. "Obviously, if this fact were known to consumers, the fact would be an important factor in making a choice between higher-priced buffered or combination aspirin products, and lower-priced plain aspirin."

In its statement, Bristol-Myers pointed out that "the commission's complaint did not say that the three products are not effective pain relievers, or that the claims of superiority over competing products are not true."

Contending that its representations that the three products are superior to other "are based on clinical and scientific studies," the company accused the law judge of "attempting to justify his ruling by introducing a new standard of proof which is far different from the 'reasonable basis' standards historically applied to the commission."

The investigation leading to yesterday's findings began in 1972, when the FTC first accused several leading analgesics manufacturers of false and misleading advertising.

The first order coming out of that probe came last year, when another judge made claims, similar to those filed yesterday, against American Home Products Corp., which makes Anacin and Arthritis Pain Formula.

That case is still under appeal. A third case is still pending against Sterling Drug, maker of Bayer, Cope, Vanquish and Midol.