JIMMY CARTER AND Leonid Brezhnev have now both said that at their summit next month they will try to squeeze some results out of what has been an interesting but preliminary Soviet-American dialogue on curbing sales of conventional arms. Their resolve is commendable, and not merely because Mr. Carter, in running for president, put an "immoral" tag on arms sales and assumed a personal commitment to limit them. Regardless of any moral angle, such sales constitute a political reality urgently needing to be addressed. The United States and the Soviet Union, the two leading suppliers, have been putting into the hands of their reputed friends and clients an ever more costly, sophisticated and frightening capacity to engage in violence on their own. Simple self-interest supplies all the reason either needs to seek restraints.

To be sure, focusing on restraints is a bit like starting out to bake a cake just with firm views on shortening: You need the whole recipe. Without a certain consensus among Americans and Soviets on their overall relationship, and sepcifically on the sort of competition they intend to wage in the Third World, no policy of restraint will get far. It is no accident that the arms-sales talks have been hung up precisely at the point where arms control turns from a matter engaging technicians into a broad foreign-policy issue. The Kremlin sought to establish general principles of eligibility to receive arms. Washington wanted to define permissible levels and types of arms transfers. When the Russians, responding to an American request to identify regions suitable for restraints, chose areas of special American interest, the talks stalled.

Even while trying to negotiate controls, the administration has been practicing what it describes as unilateral restraint. Responding to critics of its continuing heavy sales in the Mideast and elsewhere, it explains with a cough that what it has most in mind are qualitative restraints to limit "particularly destabilizing transfers." At the same time, the administration has long said, and is saying again now, that it never intended to exercise unilateral restraint indefinitely: The policy is "up for review later this year."

This is presumably a way of putting Moscow on notice, on the eve of the summit, that unless progress is made on negotiating restraints, the United States may turn to a more competitive approach. There are plenty of good reasons not to go this route. But they are reasons argued and felt most persuasively when they are respected by both great powers.