AT FIRST GLANCE, the Federal Trade Commission's decision to drop its proposed rules on the advertising of over-the-counter drugs seems curious. Federal agencies are not in the habit of spending five years investigating a subject and then giving it up without producing something. But things have changed in the years the FTC has been looking at this matter. Its action suggests that the battle for regulatory reform is not just beginning; it's already over.

Odds are that the old FTC -- the one that existed before Congress fastened on a short leash last year -- would have gone ahead with an industry-wide rule. But the new FTC, with much the same membership, is a little more cautious. If it had adopted a rule, the half-dozen or so companies that make most of these products would have charged out in fury. The courts would have examined the rule carefully to see if it violated the First Amendment, and Congress would have made sport with the idea that the federal government should be controlling ads for such things as aspirin and cough syrup.

In ducking all that, the FTC probably did exactly what Congress had in mind last summer when it rewrote the commission's charter. It looked at the record compiled during the long investigation and said the evidence did not justify a new regulation. In part, that is because of the slowness with which the Food and Drug Administration has been completing its review of the safety and effectiveness of non-prescription drugs. Without the FDA's findings, any rule on what can be said in advertisements for a whole variety of home medicines would be harder both to write and to sustain.

As it is, the FTC says it will use the evidence it has collected to attack deceptive advertising of over-the-counter drugs on a case-by-case basis. Last Tuesday, for example, an administrative law judge sustained charges that the maker of Bayer Aspirin, Vanquish, Cope and Midol had made medicinal claims for those products without reliable evidence to support them. If his finding holds up, it will have the effect of eliminating certain kinds of advertising for other products as well.

It would be neater and quicker to use an industry-wide rule to eliminate deceptive advertising than to attack claims and products one by one. The Bayer case is already in its seventh year. But the same final result can emerge if the FTC sticks to the task. Regulations will grow out of litigation instead of rule-making proceedings. Those proceedings will not be so available for foes of regulation to kick around anymore.

Such a development would put the regulatory process back where it was about 20 years ago. That should be sufficient to let the anti-regulators claim victory. The recent developments at the FTC indicate they can already start making that claim