TWO DAYS FROM now in Geneva, the superpowers will meet again "on the highest level," as the Soviets describe a summit meeting. This will be the 11th such meeting in the Cold War era, and in all likelihood, it will be a reminder that these two giants remain far, far apart, divided by deep suspicions and anxieties, ignorance and four decades of competitive relations.

Why have the Soviet Union and the United States had so much trouble finding ways to get along with each other? After four decades of Cold War, there is still no satisfying answer to that question.

Ideologues on both sides would argue that the answer is obvious -- that countries that call each other "imperialist aggressors" and an "evil empire," that espouse sharply conflicting political doctrines and regularly speak of each other as the enemy are destined to have bad relations.

But the Soviet-American relationship is more complicated and more subtle than that. These two nations are deeply divided and have spent thousands of billions of dollars and rubles arming for Cold War, but for 40 years, neither side has considered the reasons for the rivalry serious enough to fight about. For 40 years, every time a fight between the two looked possible, one or both has backed away.

This is a cardinal feature of the superpower relationship and makes it unique in the history of rivalries between great nations. The reluctance to fight can be explained in part by the cataclysmic new definition of war imposed by thermonuclear weapons but partly also by the happier fact that Soviet and American vital interests simply have not come into irresoluble conflict for these 40 years.

The persistent absence of a causus belli sometimes has curious consequences. For example, during the third year of the Reagan administration, when the Soviets were fit to be tied with frustration over the President Reagan's hard line, they launched a propaganda campaign with the ominous theme that he wanted to start a war. The campaign took hold in the Soviet Union, where women were reported in tears at political meetings at the prospect that their sons and husbands were about to be incinerated at the front.

The authorities may not have anticipated this reaction. They soon toned down the propaganda campaign and ceased comparing Reagan to Adolf Hitler, although they continued to criticize him bitterly. Then the Soviets climbed back from the limb they were on after walking out of the Geneva arms-control talks and announced willingness to resume negotiations.

It is another curiosity of the superpower relationship that, in both countries, domestic opinion seems to demand that governments keep it under control. Mikhail Gorbachev, the energetic new Soviet leader, appears determined to make some kind of success of this summit meeting, to satisfy the popular appetite for improved relations with America and to demonstrate to his comrades that he can deal with the Americans on a superpower-to-superpower basis.

Reagan has similar political requirements. As he discovered early in his first term when a combination of domestic and allied political pressures forced him to make arms-control proposals long before he originally planned to, Reagan's constituents and friends expect him to pursue better relations with Moscow. Now it is said that Nancy Reagan is pressuring her husband to make every effort to go into history as a man of peace. Every American president in the Cold War era has sought to get along better with the Soviets; Reagan came to this position later than others, but he came to it.

Yet, in the most fundamental ways, the two countries have failed miserably to manage their competitive relations. As a result, they have spent enormous sums on history's most redundant military arsenals, which contain vastly more weapons than either can ever use in any sane cause. With each new generation of more sophisticated weapons, the costs of miscalculation increase. Now, the new and apparently plausible theory of "nuclear winter" raises a serious question about whether human civilization could survive all-out war between the Soviet Union and the United States.

So the two countries that have nothing to fight about have managed to waste great riches creating weapons that no sane leader will ever choose to use. Despite the self-evident absurdity of such a situation, both sides seem fully reconciled to the prospect that it will only get worse -- more expensive and potentially more dangerous.

A geopolitical formula that underlies the bad superpower chemistry: take two large, rich, relatively isolated nations; endow each with a crusading political ideology antithetical to the other's; convince each that its well-being and stature in the world depends largely on its position vis-a-vis the other; add a large quantity of insecurity on both sides.

Was this formula destined to produce the current results? No, or at the very least, not necessarily. These 40 years have offered numerous choices, and both sides have had to make difficult ones. They often chose badly.

Fifteen years ago, Professor Adam Ulam of Harvard, one of this country's best scholars of Soviet-American relations -- a hard-liner recently invited to the White House to brief Reagan -- wrote an insightful book about the first 25 years of Cold War, called "The Rivals." Right after World War II, Ulam wrote, the United States refused to see that the real rival was "the U.S.S.R., with its problems, its strengths and weaknesses" and instead began a crusade against "godless communism."

"Even after the Cuban missile crisis," Ulam wrote, "an event which should have been a lesson as to how easy it was for the two countries to come close to agreement as well as to nuclear war, American diplomacy wanted not to strike a bargain with the Soviets but to force them to acknowledge what in American eyes were self-evident moral truths . . . ." Ulam concluded that, for a quarter-century of Cold War, American policy had been woefully distorted by "a moralistic and emotion-charged approach" to the Soviet Union.

Ulam is one of the many European-born American intellectuals who despair of Americans ever sticking to a practical, hard-headed foreign policy if offered an emotional one. That despair seems justified.

Consider the zigs and zags of American diplomacy that the Soviets have had to follow for 40 years, from the exaggerated euphoria of the "Spirit of Camp David" and the early-70s version of detente to the brinkmanship of John Foster Dulles and the evil-empire rhetoric and Strategic Defense Initiative of Ronald Reagan.

As Edward Crankshaw, the British Kremlinologist, has observed, turning the Soviet Union into a bogeyman provided the West with "an excuse to stop thinking." The consequences have not been impressive.

Not that dealing intelligently with the Soviets would be easy. Soviet leaders have proven themselves stubborn, devious and determined. They are eager to expand their influence. They have brutally seized and conquered an empire around their borders and have eagerly, if seldom very successfully, meddled in Third World nations. If Ulam's list of American mistakes is justified, so, too, would be a long list of Soviet transgressions and stupidities.

Americans have worried for four decades that the Soviets were out to conquer the world, while the Soviets -- usually much more realistic about their gaping shortcomings -- have worried about being shut out of it by the United States. Both views reflect national characters burdened by great anxieties about their own inferiority.

To this day, important Americans, including senior officials of the Reagan administration, are beset by the fear that, if this nation ever lets down its guard, the Soviets will somehow get the best of the United States, despite their grave weaknesses. And Soviet leaders continue to display a lack of confidence in their position at home and abroad, so they censor an interview with Reagan in Izvestia and try to bully foreign governments that defy their wishes, most recently the Dutch when they decided to deploy U.S. cruise missiles on their territory.

It is tempting to conclude that the counterproductive course of Soviet-American relations over these 40 years has served profound psychological and political needs on both sides, even if its practical consequences appear to leave both countries worse off and less secure than they needed to be. The United States, a compulsively competitive society, wanted an adversary worthy of itself and invented one for about 25 years until the Soviets could build enough weapons to live up to the image. The Soviets needed an "imperialist" adversary that could satisfy their deeply ideological perception of the world, and the United States filled the bill.

But so far, neither side has demonstrated a need to fight a war. On the contrary, by the standards of past international rivalries, they have taken unprecedented steps to reduce the danger.

The treaty to prevent incidents at sea, first signed in 1972, may not sound dramatic, but it represents a unique and remarkably successful effort to control the two nations' rambunctious navies. The series of arms-control agreements from the atmospheric test ban to SALT II have kept the arms race within controlled boundaries and made the world slightly safer, as even Reagan seemed to acknowledge by embracing SALT II in office after decrying it in the 1980 campaign. The Washington-Moscow hot line, recently upgraded, is an intriguing symbol of limits both sides hope to put on Soviet-American hostility.

During these 40 years, both countries have changed. When all this began, Josef Stalin ruled Russia; now, it is in the hands of young technocrats who have finally acknowledged the failure of the Soviet system to compete. The United States is more realistic about the "Soviet threat," and even Reagan is eager to sit down with his Soviet counterpart at a conference table.

Whatever transpires across that table will not soon transform this difficult relationship. The underlying suspicions and anxieties remain, and it is vastly easier to continue as before than to change course. The intriguing question is whether these two behemoths can ever break out of the counterproductive relationship in which they have been locked so long. Intriguing, but it will not be answered in Geneva.