Since the American withdrawal from Vietnam, the Soviet Union has become much more active in conflicts in the third world. Through varying degrees of military involvement, Soviet foreign policy has gained Marxist-Leninist allies in Angola, Mozambique, Ethiopia, South Yemen, Cambodia, and Afghanistan.
However, the Soviets have also experienced several important failures in the third world; they have lost important allies such as Egypt and Somalia, among others. Further, in some third-world nations where Marxist-Leninist governments have come to power, strong local opposition to them has developed. Even with Soviet, Cuban, or Vietnamese assistance, the rulers of Angola, Ethiopia, Cambodia, and Afghanistan have not yet defeated their armed opponents.
What can be said about Soviet foreign policy intentions in the third world? Are they basically offensive or defensive? Is the USSR bent on military expansion in the third world, or is it merely trying to maintain its position there by acquiring new allies as old ones break away from it? Answers to these questions may be sought through examining what the Soviets themselves have said about the third world over time.
During the Khrushchev era, the Soviets were highly optimistic about the spread of their brand of socialism in the third world. Despite United States military superiority, Khrushchev believed that the new nations would voluntarily become Marxist-Leninist allies of the USSR. This process was seen as occurring naturally with only a small degree of Soviet effort being necessary to help it along.
During the early Brezhnev years (1964-68), this optimism was dampened. Several ''progressive'' third-world regimes were overthrown in right-wing military coups, as in Ghana, Mali, and Indonesia. Further, the American buildup in Vietnam threatened to defeat communist aims in Indochina. The Soviets concluded that greater effort on the part of the USSR was needed to maintain third-world nations on the intended path. This greater effort included Soviet military assistance when necessary. Nevertheless, the military role of the USSR was intended to be of an auxiliary nature; the main burden of any fighting was to be borne by local Marxist forces.
The middle Brezhnev years (1969-75) saw the resurgence of Soviet optimism. America withdrew from Indochina, the Portuguese empire collapsed, and many third-world nations acquired Marxist regimes. The Soviets assumed that the decline of Western influence in the third world would lead to a corresponding rise in Soviet influence there. They believed that only low-cost, short-term Soviet military efforts were needed. The USSR acknowledged sending not only weapons but also Soviet advisers. Even then, the USSR would only play a supporting role while local Marxist forces would undertake the bulk of the struggle to establish and maintain socialism.
During the late Brezhnev years (1976 to the present), Soviet optimism has given way to increasing pessimism. Two important Soviet allies, Egypt and Somalia, abrogated their treaties of friendship and cooperation with the USSR. In addition, pro-Soviet Marxist governments that had recently come to power faced strong local opposition.
It soon became apparent that these new Marxist-Leninist governments could not remain in power through relying on Soviet arms transfers and advisers alone - they were simply too weak. The main burden of the fighting would have to be undertaken by the established communist states, such as Cuba in Angola and Ethiopia, Vietnam in Cambodia, and the USSR itself in Afghanistan.
Yet even with such direct military intervention, the opposition to the new Marxist-Leninist regimes has not been readily defeated. It is now clear even to Moscow that it and its allies must undertake high-cost, long-term military efforts just to maintain these new regimes in power.
The Soviet Union has seen that its third-world allies which are not completely Marxist-Leninist tend to break away from the USSR after a while. Further, Soviet allies that are thoroughly Marxist-Leninist tend to be weak and to arouse armed opposition. This opposition, though, does not stem from the West but from indigenous forces. This is perhaps the bitterest blow to the Soviets - while they always knew the West would be their enemy, they expected the third world would not. It is for this reason that the Soviets during the late Brezhnev years have come to view themselves as being on the defensive in the third world.
Yet how can this be said when they are now ''defending'' nations such as Afghanistan which did not come under Soviet influence until very recently? The Soviet Union has a strong interest in seeing that a Marxist-Leninist government, having come to power, does not fall. Should one such government ever be overthrown, then others might become more vulnerable and fall, too. The fact that this might occur at the hands of indigenous third-world forces, and not the West, would reveal that the USSR and Marxism-Leninism hold little attraction for the people in the third world - exactly the opposite of what the Soviets have always claimed.
Although the relatively costly and protracted military commitments directly undertaken by the USSR and its allies in Angola, Ethiopia, Cambodia, and Afghanistan have not yet proven successful, so far they have not been overwhelmingly burdensome to the Soviet socialist community. But if the opposition to Marxist third-world governments became militarily stronger, or if serious indigenous opposition erupted in other Marxist third-world nations such as Mozambique, South Yemen, or even Cuba or Vietnam, the problem the USSR faced would be greater.
The USSR would then have to decide between two courses of action: (1) making a much greater military effort itself to defend existing Marxist regimes, which would assure greater opposition to its foreign policy from both the West and the third world and would risk the possibility of domestic opposition within the USSR against the economic and military burden such a policy would entail, but would not guarantee that such a policy would be any more successful than it has been so far in Afghanistan; or (2) allowing Marxist third-world governments to be overthrown (not just letting incompletely Marxist-Leninist allies such as Egypt and Somalia change their minds) where they are strongly opposed by indigenous forces. This would risk the encouragement of opposition to other Marxist third-world governments that would also have to be allowed to fall without the USSR undertaking a major military effort to save them, and perhaps eventually risk the growth of political opposition within the USSR itself.
If this is indeed the choice that Soviet foreign policy faces in the future, it will be evident that Soviet hopes that the third world would willingly accept the USSR as a model for its own economic and political development were woefully optimistic and will never be fulfilled.Mark N. Katz is currently associated with the Brookings Institution. His book ''The Third World in Soviet Military Thought'' will be published in mid-1982.