The rule in our society -- a fundamental and distinctive feature of our system -- is that the military should not be used to enforce the law. That limiting tradition is as important to the military as to citzens concerned with civil liberties. The few familiar exceptions come in times of great duress: to patrol after natural disasters, to put down riots, the occasional use of troops in the 1950s and 1960s to enforce civil rights.

Now there is talk of a new exception: expanded use of the military to block drug traffic into the country, particularly from Latin America. Adm. James D. Watkins, chief of naval operations, reports that the Joint Chiefs of Staff have unanimously recommended it. If the producing countries were willing, the services would help them train teams nd lend or sell them equipment to suppress production. U.S. planes and ships would also step up surveillance -- the services already do some, as adjuncts to the Coast Guard -- to block the shipment of drugs. "It could be a rallying point for this hemisphere," the admiral said.

It is a tempting idea. Drugs are a curse, and our law-enforcement agencies lack the resources to do much more than nick the trade. It would help enormously to have the military -- and foreign governments -- actively on their side. The dollar cost to the military would be relatively low. The surveillance would be good exercise; presumably it would not be allowed to detract from other military missions.

The problem would be to keep it that simple. Drug interdiction should not be intertwined with other issues. Adm. Watkins suggested the drug trade was helping to finance leftist insurgencies in the hemisphere, making the trade "a national security problem" and so a legitimate target for the military. There is no need for that kind of coloring; the drug trade is bad enough on its own. Whatever the military is asked to do about drugs ought to be kept separate from what it is asked to do in other areas.

A second complication involves what the military would do. The chiefs would have the military act only as a kind of spotter for law-enforcement agencies. Others think the Navy should actually stop, search and seize; a pending amendment to the defense bill in the House would empower it to do so. That, too, is tempting, but the proposal has not been thought through. Against whom would the military use force, under what rules, in what places, on what legal grounds? Good answers are needed before Congress votes. The reason the amendment is attractive is that the military is so powerful. That is also precisely the reason why the military is so sparingly used in this country.