Understanding the Soviet threat; The Soviet Union and SALT, by Samuel B. Payne Jr. Cambridge, Mass.: MIT Press.

This slender book deals quite brilliantly with a subject of transcendent importance: the nature of the Soviet threat. Carried one step farther, this enormous subject leads to a question: Must the US maintain nuclear parity -- or even superiority -- in order to minimize the danger of a world holocaust?

In order to gain insight into these matters, Professor Payne, political scientist at Ferrum College in Virginia, has made a study in depth of Soviet propaganda and domestic publications. His conclusions are of overwhelming relevance today.

According to Payne, the Soviet elite is split into basically two groups: the militarists and the arms controllers. These two factions are in broad agreement on ultimate aims, for both look to ultimate Soviet domination over the adventurism, "irremediable decline and slow despair" of the imperialist world. Both agree that the USSR must operate from strategic parity with the US at the very least.

It is in his understanding of the areas of controversy -- chinks in the monolithic Kremlin faccade, if you will -- that Payne is both fascinating and important:

* The militarists believe that the US is reckless and aggressive.

* The arms controllers believe that there are "sobersided" elements here that recognize the necessity of accommodation.

* the militarists are convinced that a preemptive first strike by the "aggressor" (the US, in their lexicon) is possible.

* The arms controllers think such a strike unlikely.

* The militarists hold that the Soviet economy can sustain a continuation, even an increase in their great expenditure on military needs and at the same time improve consumer demand. In brief, that guns andm butter are possible.

* The arms controllers maintain that a levelling-off of weaponry -- a cooling of the arms race -- is very much in their national interest.

Fortunately the decisionmakers at present are Brezhnev and other aging leaders hho do not seem to accept "a preemptive strike strategy." Payne cites considerable evidence that they believe a nuclear stand-off, rather than the costly pursuit of superiority, may well lead to the bargaining table.

We must remember that such sanguine opinions as these are conditioned by Brezhnev's health and age, and by the fact that our own policy seems to be hardening by the day into a cold-war freeze.

Payne's title derives from his analysis of Soviet writings on SALT I and SALT II. What is omitted there as well as what is said has significance. For instance, the militarists were very careful not to criticize SALT I, since it found favor with the highest authority. But the sparsity of coverage is in itself evidence of disapproval.

By contrast, the arms controllers give both SALT agreements broad acceptance. Yet it should be noted that these statements are invariably presented as imperatives springing from Soviet strength and US weakness. And so, Payne's reminds us, will it always be.

Now that an American antiballistic missile (ABM) system is reported to be under consideration again, it is interesting for us to learn how sharply aware the Soviets were of its value as a bargaining chip during SALT I. The fact that it was later ruled out as too costly and largely unworkable was irrelevant: To them it posed the threat of a technical breakthrough which could have made a preemptive US strike less vulnerable to counterattack.

(There's a lesson herein for Eugene Rostow and other future bargainers: The less advanced a threatening system is, the better it serves as a bargaining chip.)

Professor Payne's book went to press last year before he had access to Ambassador Gerard Smith's splendid account of his stewardship in negotiating SALT I in his book titled "Double Talk." But Payne's research into Soviet sources and his developed intuition are confirmed in good degree by that larger, more detailed book.

Here is the heart of the matter as Smith learned it on the front line and Payne states it in his book:

"Arms control should not be linked to the overall relationship between the US and the Soviet Union. We should not make an arms control agreement contingent on the resolution of our conflicts with the Soviets in other areas, nor should we expect an arms control agreement to make Soviet policy in general less hostile and aggressive. . . . To make a change in Soviet policy in the Mideast, for example, a prerequisite for arms control negotiations is, in effect, to ask the Soviets to repudiate their concept of peaceful coexistence, the foundation of their foreign policy. Neither arms controllers nor militarists would accept such a demand. . . .

"The strategic arms limitations negotiations show also that American willingness to spend heavily on armaments is necessary for American success in arms control negotiations. The Soviet leaders are deeply power-oriented people whose conduct of any negotiations with a foreign country is largely determined by the relative power of that country and of the Soviet Union. if the American government negotiates with them from a position of strategic inferiority, then the Soviets will accept only an agreement that confirms American inferiority and primarily meets the needs of the Soviet Union. The United States can through arms control negotiations restrain the arms race and reduce military spending, but, paradoxically, only by being willing to spend heavily on armaments if the negotiations fail."

What the informed citizen can learn from such books as Professor Payne's is that negotiations is the best hope on earth, and per haps the last.