(FORTUNE Magazine) – What should American policy toward the Soviet Union be? Nobody can answer that question without confronting another: What are Soviet intentions? I am not referring to short-term, tactical intentions of the kind that an intelligence network might uncover. It would be nice to know these, of course, but unless we get an agent into the Politburo, we are unlikely ever to know about such matters. The Soviet government is secretive in its deliberations and, like other governments, often has no clear idea beforehand about how it will respond to unforeseen opportunities or problems. The American decision to invade Grenada was made within a few weeks; the Soviet decision on Afghanistan may have been similarly abrupt. And since the Russians don't know what they will do in particular circumstances, it is futile to insist -- as Congress and the media continually do -- that our CIA ought to know. But if we cannot answer many questions about Soviet intentions, we can answer one big question: What do the Soviets themselves conceive to be the purpose of their foreign policy? In answering that question one needs a knowledge of Russian history and Communist party history, the essentials of Marxist-Leninist doctrine, and even some familiarity with the history of religious and ideological movements. It also helps to have known some Communists at first hand. None of these will help the State Department cope with daily crises, but they make it possible to identify the ''nature of the regime,'' as political scientists would put it. They afford insights into what is possible and impossible for the regime to do, as distinct from what it is likely to be doing tomorrow. Understanding the Soviet regime has been made unnecessarily difficult by an extraordinary amount of wishful thinking among Western scholars, publicists, and statesmen. Wishful thinking abounds because in a nuclear age international tensions between the superpowers can be so intimidating. A mostly useful antidote to wishful thinking is The Soviet Paradox: External Expansion, Internal Decline ($22.95, Knopf), by Seweryn Bialer. As a young man Bialer was a member of the Polish Communist party. For the past 20 years he has been on the faculty of Columbia University's School of International and Public Affairs. He has now given us a rounded picture of the Soviet Union -- its economy, its society, its political system -- since the Stalinist era. Alas, in his final chapter, on U.S. policy toward the Soviet Union, he evidences exactly the kind of wishful thinking that is now so pervasive in academic circles. But until he gets to U.S. policy, he is at once masterful in his command of the subject and lucid in his exposition. Bialer has organized his material chronologically, Soviet leader by Soviet leader, analyzing the conflicts within the Politburo as best a sophisticated Kremlinologist can perceive them. The tone is cool, detached, hardheaded, avoiding both polemics and apologetics. The picture that emerges will have few surprises for anyone who has been paying attention to Soviet affairs. Winston Churchill to the contrary, the Soviet Union has never been ''a riddle wrapped in a mystery inside an enigma.'' We know that it has a centrally planned economy capable of doing certain things reasonably well -- the kinds of things that can be accomplished by issuing commands, like producing large numbers of tanks. It cannot, however, satisfy the Soviet consumer, whose ''needs'' are defined from above and whose ''wants'' are not seriously considered. AS BIALER MAKES clear, this economy cannot be reformed or liberalized in any significant way. To allow private enterprise a larger share would, over time, create centers of power intolerable to a totalitarian system. More important, tolerance of private enterprise would threaten the integrity of the official socialist myth, which holds that all Soviet citizens have been liberated from the shackles of capitalism and are freely devoting themselves to the public interest (as defined by authority). The Soviet Union has had spasms of liberalization -- indeed one spasm lasted for most of the Twenties -- but these have to be viewed as ad hoc responses to severe economic difficulties, and such policies are always abandoned. Soviet society is marked by a sullen passivity among the general population and pervasive cynicism among the intelligentsia. It is a society in which, Bialer tells us, a recent slogan plastered on factory walls reads: ''It is insufficient to be at work, it is necessary to work.'' It is a society whose best poets and novelists are published only in the West. Even in the area of Marxist scholarship and theory, little of interest has come out of the Soviet Union. The country hasn't produced a biography of Marx or Lenin that Western scholars need to take seriously. And above this economy and this society is the Communist party, encompassing perhaps 10% of the adult population. Most Communists, of course, are typical Russian bureaucrats, manifesting high levels of corruption and inefficiency and low levels of active political concern. But for party members at the higher levels, commitment to the regime is serious and unqualified. This is their regime, and they identify with it in an unreserved way. Is the commitment truly doctrinal? Is the ruling elite of the Soviet Union composed of true believers in Marxism-Leninism? Or must we view this doctrine merely as intellectual baggage inherited by the elite but not to be taken seriously? The question tantalizes many Western analysts, since its implications for U.S. policy seem so weighty. Are we dealing with a Soviet Union whose foreign policy is mainly an extension of Imperial Russia's? Or a Soviet Union in which messianic Marxism-Leninism -- requiring the destruction of the entire bourgeois world -- is central to foreign policy? In fact the debate is pointless. We know that the Communist party of the Soviet Union is headed by Russian nationalists. Why on earth shouldn't the party leaders be nationalists? And why shouldn't they, like Communists elsewhere, use nationalism to secure popular deference to their policies? Why not, as they do, call World War II ''The Great Patriotic War''? But we also know, and not only from the many high-level Communist defectors who have told us so over the years, that the Soviet leaders are Marxist-Leninists. They may have read little Lenin and less Marx. (Bialer suggests that Mikhail Suslov, who died in 1982, was probably the last Politburo member to have made it through even the first volume of Marx's Das Kapital.) Yet the Soviet leaders think like, talk like, and act like Marxist-Leninists. Does this mean that Gorbachev actually believes, in his heart of hearts, all the dogmas of the Marxist-Leninist creed? The question is absurd. It is like asking whether Louis XIV believed all the dogmas of the Catholic Church. Of course he believed in all of them, even though he may never have known most of them, and even though he violated some of them when it suited his purpose. He would not have been Louis XIV otherwise, just as Gorbachev would not otherwise be general secretary of the party. As for what goes on in his heart of hearts -- it seems doubtful that anybody achieving absolute power in the Kremlin can afford to have a heart of hearts in the first place.

All of which is made clear by Professor Bialer. He notes the sensitivity of the Soviet leadership to criticism that has an ideological dimension -- as in Ronald Reagan's ''evil empire'' speech, for example. He notes the leaders' concern about various neo-Marxist ''heresies'' now flourishing in some Western intellectual milieus. Clearly, the Soviets profoundly fear anything that subverts their ideological legitimacy, meaning their very title to rule. ! Which brings us to the ''paradox'' of Bialer's title. The term refers to the Soviet Union's curious-looking blend of failure and success. On the one hand, an economic system doomed to work badly. On the other hand, an expansionist and assertive foreign policy backed by the regime's enormous success in creating military might and attaining superpower status. It might seem reasonable to ask how long the two themes can coexist. After all, being a superpower is awesomely expensive. One might suppose the leadership was endlessly under pressure either to change the economic system or change the foreign policy. How long can the ''paradox'' endure? Oddly enough, Bialer does not tackle this question head-on. The paradox in his title is much muted in his analysis. Indeed he seems not to take the title seriously, for the implication of the analysis is that there really is no paradox. The basic purpose of Soviet foreign policy, he persuades us, is to preserve the Marxist-Leninist regime. The regime can derive no legitimacy from its economic performance or, of course, from popular consent. So its claim to rule must rest on its performance in the arena of foreign affairs, where it can mobilize patriotic and nationalist feelings on its behalf. Without continuing, demonstrable successes in foreign policy, the Soviet Union would look somewhat like a giant Yugoslavia, stumbling ineptly from one internal crisis to another. SINCE BIALER'S analysis is sensible and does a lot to explain the imperatives that shape Soviet foreign policy, it is all the more puzzling that his final chapter suddenly diverges into the most conventional kind of State Department chatter. It features tired rhetoric about ''normalization'' of relations, in which ''elements of competition and cooperation are better balanced.'' Bialer believes that ''crisis management'' is a fine idea and arms control a positively splendid idea. He wants the United States and the Soviet Union to seek ''parity rather than superiority'' in military strength. The ending simply doesn't go with the rest of the book. Given Bialer's perspective on the nature of the regime, the reader has no reason to think the Soviet leaders are interested in either parity or cooperation. Or to suppose that ''normalization'' will ever be possible so long as Marxism-Leninism is the legitimizing creed of the Soviet system.