AFTER 10 YEARS of consideration, the Federal Trade Commission has finally come up with a decision in the cases attacking aspirin ads. The commission ruled that the companies must produce substantiation--scientifically valid evidence--if they claim that tests have proved their product superior to its competitors. But if an ad simply states that a product is superior, then scientifically valid evidence isn't necessary. In such cases, the commission majority says, consumers have no reason to think the statement is based on scientific evidence, and so won't be misled if, in fact, there is none.

That's certainly debatable. Two commissioners dissented on this last point, which overruled a 1981 FTC decision in another pain-reliever case. They argue that in this era of regulation, consumers expect that the government requires proof of all advertised claims about drugs--and that therefore such proof should be required. But, as all five commissioners agree, no one is really sure what consumers expect.

That may sound like splitting hairs, but it's a serious issue. Big money is involved. Aspirin is among the most heavily advertised of products, because there's little difference, so far as anyone can tell, between different brands--except their ads. So a well-designed ad campaign may be worth millions in sales. Commissioner Michael Pertschuk suggests that scientific proof that one of these products is better than another will always be lacking, and it's not a long step from there to a rule that bans all advertising for pain relievers. But no one advocates that. So there will likely be more ad campaigns, more challenges by regulators, and more decisions that will have to be made, as Commissioner Patricia Bailey points out, on the finest of distinctions.

All this would be disturbing if you believed, as some writers in the 1950s argued, that Americans are putty in the hands of television advertisers. It's true that ads do help sales of some products, particularly those like aspirin in which there's little difference between brands. But if exhortation could automatically produce obedience, we'd all still be buying American cars every two years. The FTC is right to protect the consumer against outright deception, but it shouldn't strain to extend its theories so far that they end up banning advertising altogether.