In this age of computer-guided rockets and Buck Rogers wonders of destruction, something terribly primitive remains fixed in the rivalry of the world's two nuclear superpowers.

Us and Them. America and Russia. The Soviet butchers. The imperialist warmongers. Primitive fears, crude reflexes, ancient rituals of faith are invoked to ward off unseen demons.

These two great nations do at times behave like two primitive tribes living in adjoining valleys, worshiping different gods, each fearful of whatever it is that lurks just over the mountains. When one tribe hears rumblings of warlike noises, flashes of lightning from the mountain, warrior chiefs arouse the people and scientist priests summon new magic weapons, like ancient totems, to protect the faith.

Crudely speaking, the modern arms race reflects those ancient patterns of behavior. The rivalry is real; so is the hostility.But, in the history of human kind, these struggles usually end in warfare and so now we face a new dilemma - and twin threats of the "enemy" tribe and the nuclear threat of our own destruction. History asks: "will this story end in the same old way or will these two nations find a way to break out of that primitive pattern?

In our society, as in theirs, it is taboo to think of the "enemy" as any thing but the enemy (though the penalties are quite different: an American politican is defeated for being "soft on communism;" a Russian dissident is sent to prison). But the current strategic-arms debate poses an implicit question: to what extent can Americans and Russians set aside the "enemy" ideology, their alien faith, and consider our mutual self-interests, our shared human values, reflexes, limitations?

The strategic debate rarely addresses that theme directly - it is politically damaging to do so - and yet it is implicit in almost every calculation, every alarm over new scenario, weapons.

This season, as so often before, the conflicting approaches are at war just beneath the surface of the dialogue. President Carter urges cooperation with the Soviets toward mutual arms reduction. Yet a broad array of deeply-troubled skeptics warns with facts and figures that the Soviets are bent on destroying us - that new and dangerous rumbles have been heard from Moscow.

This season, the new rumble is a civil defense gap.The Russians, it is said, are preparing at great expense fallout shelters and evacuation plans for their population. Why would they bother if they were not serious about the possibilities of nuclear war? A good question Serious people argue over it, from both sides. Americans will be hearing much more on the subject, as the strategic-arms debate plays out on various weaponry issues in the months ahead.

A few forceful proponents have made dire predictions about the answer to that question. Maj. Gen. George J. Keegan, former Air Force intelligence chief, for one, fears that the Soviet civil defense program was "the decisive turning point in my judgment that we (have) already lost the strategic balance."

Paul Nitze, in his influential essay last winter in Foreign Affairs, said the Soviet Union is spending $1 billion a year on civil defense (compared with $80 million here) and Nitze cited soviet manuals from 1969 and 1970 which assert that no more than 3 to 4 per cent of the population - a mere 10 million Russians - would be killed in a U.S. attack.

"The Soviets may well overestimate the effectiveness of their civil defense program," Nitze conceded, "but what is plain is that they have made, for 20 years or more, an approach to the problem of nuclear war that does assume, to a degree incomprehensible to Americans (or other Westerners), that nuclear war could happen, and that the Soviet Union could surivie."

An associate of Nitze's, T.K Jones of Boeing, has since calculated the question more closely and made ominous projections about what the Soviets might be doing. The Soviets, he asserts, "can protect their industry and facilitate its rapid recovery should a nuclear war occur . . . can protect their work force . . . (and) protect their indutrial machinery . . ."

"It makes my blood run cold," said Nitze, who mentions Jones' study without quite embracing its conclusions.

Among other things, Jones has determined that the Soviet Union could recover from a nuclear war "within no more than two to four years, whereas the U.S. could not recover in less than 12 years.

Even if Russia were to lose half of its population and all of its industry, Jones claims, it could recover its prewar gross national product within 15 years. As one arms-control advocate pointed out, this would amount to doubling the per-capita GNP for the Soviets in a very short period - a feat which they have had trouble doing without nuclear war.

When Science magazine asked Jones how much bunker-building and factory protection the Russians are actually doing, Jones' answer was, not much.

"But," he told Science, "I just have this cold, sinking feeling when I think about how much there might be that we don't know about."

As Nitze's article suggested, the adherents of the civil defense gap believe the Russians do not accept our view that nuclear war is virtually unthinkable. Instead, these people warn, the Russians are seriously prepared to fight and win an all-out nuclear war.

One indication of this, they say, is the Soviet Union's civil defense preparations: protection of some industrial installations against the hazards of blast and fallout, underground installations to save the country's leadership, underground food reserves and published plans to disperse the population if an attack is threatened.

The civil defense gap theory provokes extraordinarily strong reactions within the community of people who make it their business to follow and participate in the ongoing debate about strategic issues. While Nitze or Jones talk freely of possible Soviet preparations for nuclear war, experts with equally good credentials ridicule the entire idea as "a joke" or "ridiculous."

So when the alarm-sounders cite Soviet rhetoric about the plausibility of a nuclear war and Soviet capacity to "win" it, their critics cite other pieces of Soviet rhetoric which refer to a superpower nuclear war as "suicidal." The critics also note that American military literature abounds with references to fighting and prevailing in a nuclear war. Does that mean we are preparing to fight one?

Moreover, the figures produced by Jones to support the proposition of a speedy Soviet recovery from nuclear war are by no means the only figures available. A decade ago, for example, the Pentagon made these calculations on the potential destructive force of U.S. hydrogen bombs dropped on the U.S.S.R.:

Four hundred equivalent megatons could kill 74 million Soviet citizens and wipe out 76 per cent of Soviet industrial capacity. Eight hundred megatons could kill 96 million people; 1,600 megatons could kill 116 million.

The United States, according to one congressional estimate, now has about 4,200 equivalent megatons ready to deliver against Soviet targets.

But the "civil defense gap" raises broader questions about the nature of the enemy. Given the invulnerability of America's capacity to strike back, to level Russia's great cities, it is plausible to think that the Soviet leaders might risk the destruction of all the have built since World War II?

W. Averell Harriman, the elder statesman, one of the first to warn of Soviet hostility following the war, describes the present alarms as "this orgy of Russian terror," which obscures obvious realities about Russian society.

"Go to Leningrad," Harriman suggested. "Never in the history of the world has there been such a dedication, a determination to reconstruct the past, the imperial palaces. They're just determined to see that the German invasion will not take away any of their heritage. To think that the same people are planning a war that would bring atomic bombs down on them there and destroy everything that they have built - it doesn't make sense."

The alarmists do not reject that view so much as they reject the certainty with which it is expressed. What if Harriman is wrong? They would ask. Can we risk a mistake that could destroy the United States?

This is the frame of mind that has always dominated the American strategic debate. Prudence above all; take no risks. Defense Secretary Robert S. McNamara took this even farther when he invented the notion of the "greater than expected threat" - a danger from the enemy greater than any evidence suggests is possible.

This sort of prudence seems to lead in only one direction - toward more and better weapons.

Critics of the "worst case" view of Soviet civil defense programs argue that this time, at least, we can be realistic without being imprudent. They raise many challenges to the alarmist view. For example:

Aren't there some targets in the Soviet Union which, if destroyed, would cripple the economy and invalidate optimistic projections of a speedy postwar recovery?

One of these might be the headquarters of the State Planning Commission in Moscow, whose files and computers guide virtually every aspect of the centrally planned economy. Another might be the country's oil refineries, which - according to congressional staff analysts - cannot be protected against nuclear blast. Yet another, proposed in a recent article in Orbis magazine, might be the dams and drainage systems in Soviet farm regions. Without them millions of acres of fertile land could be turned into marshes and desert.

Is mass evacuation of city dwellers into the countryside a realistic possibility?

The "worst case" scenarios predict that city dwellers could go into fields and forests, where they would dig makeshift shelters and stay for the duration of the nuclear exchange. But what about the weather? The Russians winter can last six months; in spring and fall the countryside is awash with mud. Is the Soviet Union counting on a civil defense system usable only for a couple of months in summer?

Would victory in a nuclear exchange have any value?

The alarmists discuss the possibility in terms of the two superpowers and the relative speed with which they might recover from a nuclear war. But a "victorious" Soviet Union could easily emerge weaker than China, weaker than Japan, weaker in relation to the restive East European satellites. Would those countries voluntarily remain subservient to a crippled Russia that was unable to provide the oil and raw materials it now sells them? For that matter, would Estonia, Latvia and Lithuania?

(Asked about the effects of nuclear war on the Soviets' superpower status, Jones replies that in his scenarios the Russians would emerge from nuclear war with substantial military superiority over all other world powers, so the Soviets could still intimidate their neighbors, and even coerce the United States and others to provide food, machinery and other things needed for recovery.)

The most plausible explanation for the Soviet civil defense program would appear to be the Chinese threat, in the view of many scholars. China has a primitive and limited nuclear arsenal. The Chinese and Soviets have already fought along their long border, and animosity is deep.

The Soviet shelter system "would be useful under certain circumstances against the Chinese," according to the Federation of American Scientists - even if it would not assure much protection against an all-out American attack.

There are other possible explanations. Senior CIA officials have suggested as one means of mobilizing the population, a tool which unelected leaders employ to instill a useful degree of fear. It helps remind the often undisciplined population that the country faces a constant foreign threat - that vigilance is a duty.

Examined closely, the Soviet Union's mailed fist is wrapped around some embarrassing weaknesses. For example, this is a superpower that cannot be traversed on a paved road - none exists that crosses the U.S.S.R. Its technology is often primitive. With a few exceptions, the Soviet civilian economy is 25 years behind ours in computerization. Soviet productivity is poor, and the Russians must turn to foreigners for basic economic inputs - the capacity to build passenger cars and trucks, and cups and saucers.

American farming makes up less than 3 per cent of our gross national product, yet U.S. productivity is so abundant that it can bail out failures in the Soviet Union, where agriculture is 17 per cent of the GNP.

In short, Soviet leaders have lots of good reasons for feeling inferior. Yet their ideology promises that someday Marxism-Leninism will overrun the "decadent capitalists" and reign supreme. How does one keep the Soviet faith when reality promises a long future as No. 2 in most spheres of modern life?

Military hardware is one area where the Soviets can catch up, crudely, at great expense, but still it is a psychic comfort, important to their ideology and their self-esteem.The Kremlin leaders wish to tell themselves, their people and the world that they, too - like the rich Americans - are second to none.

If fear and insecurity are major motivations for Soviet arms-building (as opposed to some active design to this perspective opens new questions for Americans to answer about their own self-interest. Is it in America's world's, to lead the Soviets off on another chase, another round of unlimited arms building? Once the Russians have satisfied themselves on nuclear parity with America, do they have mutual motives for arms reductions, domestic pressures which might be more compelling and exploitable if the arms race abates?

The strategic debate deserves to be widened. By counting only weapons, and ignoring the other aspects of Soviet society, the West credits the Russians in the only category in which they can compete, ignoring the many others where they cannot.

"The intelligence community will not look at the hard analytical questions which can't be answered precisely," an arms control official complained with despair. "Why do the Russians say what they say rhetorically? Why do they deploy so many different [weapons] systems? Why do they buy what they buy? What's the relationship between the political leadership and the military bureaucracy? What are their true strategic intentions?"

In short, Americans have to ask, less passionately, more objectively: what is that tribe on the other side of the mountain really like?