If you were wary about life SALT but ready to give it a try you will be dismayed by life without SALT, which is what we now face for an indefinite while.

Life with SALT meant worrying if the Russians were gaining a strategic edge, but life without SALT means doing without an Formal agreed restraints on arms-building -- restraints that, pro and con experts agree, would bear more heavily on Soviet programs in the works than on American programs. In particular, without SALT the Kremlin is free to add to its missiles the extra warheads that could theoretically ensure they could kill our land-based missiles in their silos.

Life with SALT meant asking whether the Russians might cheat on those agreed restraints, but life without SALT means denying ourselves a whole set of proven procedures for checking not only on Kremlin cheating on SALT but also on what missiles it's planning and deploying overall.

Life with SALT meant arguing among ourselves whether the Russians were using our interest in arms control to blackmail us into countenancing their burglaries in the Third World, but life without SALT means removing all formal nuclear restraints precisely at the moment when Third World tensions promise to push the United States and the Soviet Union toward successive confrontations in that troubled region.

All this is, of course, pretty obvious. It is what led Gen. Lew Allen Jr., Air Force chief of staff, to say the other day that although the treaty is now in political ill health, it remains in the common interest because it caps the strategic weapons of both sides. Since his earlier endorsement was not based in the slightest on trust of the Kremlin, Allen added, the Afghan affair did not alter his judgement of the treaty: "The logic of it is such that the American people will return to it."

Plainly, Jimmy Carter hopes this is so. As he redrafts his foreign policy to conform with sharper perceptions of the Kremlin, SALT is the one big element he does not wish to change.

It will not be easy to persuade people that it is desirable, or possible, to make a safe, effective arms agreement with the invader of Afghanistan, but with the help of sane voices like that of Gen. Allen, it should be manageable.

Some of the leading anti-SALT rationales, moreover, have been dulled. It can no longer be fairly claimed that a defeat of SALT is essential to shock the public into recognizing the Soviet threat, for the public has been so shocked. Nor can the treaty still be legitimately held hostage to defense increases and a toughening of foreign policy, since these have come about, too.

A smart president will not claim that SALT builds detente or keeps trouble from the door or saves money or anything sounding goody-goody like that. He will simply say that SALT can add an appreciable margin of safety to the rough and tumble that Washington and its friends are likely to be conducting with Moscow and its friends at least for five or 10 years. That's plenty.

But what kind of SALT? That's the main unanswered question Carter and the rest of us must address.

Basically, two kinds of SALT are possible. One, based on the idea of mutual deterrence, aims at allowing each side to preserve the forces with which it could deliver a country-killing second strike if it were hit first. The second, based on the idea of parity or "essential equivalence," simply tries to balance out the different types of missiles the two sides have, whatever they are, as equally as possible.

There are a lot of reasons why SALT was foundering before Afghanistan; but if there is one heavy and serious reason, it lies here. Carter never made clear that there are two kinds of SALT and he never got either kind straight.

When he argued deterrence, he did not explain how deterrence would work if both the Soviet Union and the United States were building (as they are) the silo-busting missiles that would allow either of them theoretically to take out the other's principal force in a first strike. By arguing deterrence, however, he seemed to be saying that parity didn't matter that much, and this hurt him when he argued parity.

When people do start turning again to SALT, they are not going to want to pick up where they left off. Afghanistan will make them -- should make them -- appreciate SALT more, but it should also make them demand more of SALT in the sense of knowing just what the process really offers to the security of the United States.Carter, or whoever's president, should be ready.