CANDIDATE RONALD REAGAN promised to stop "Soviet expansionism." As president he has diligently re-oriented American foreign policy toward the Third World with this in mind. Secretary of State Alexander M. Haig Jr. is travelling it. the Middle East this week to convince Arab and Israeli leaders to put aside their differences and unite against the Soviet Union. The administration has analyzed unrest in Central America quite graphically: a few weeks ago. Haig told a Congressional committee that the Soviet Union and Cuba had drawn up a "hit list" of countries in the region.

Certainly, a foreign policy based on "thwarting Soviet expansionism" is easier to understand and justify than the diffuse, human rights-based strategy of the Carter administration. Yet while an orthodox, bipolar approach may be a effective basis for relations with the developed nations. e.g., Japan and Western Europe, such a strategy is inappropriate for the Third World. Furthermore, the administration seems to be ignoring the economic imbalances that have generated discontent in the Third World, facilitating the growth of Soviet influence.

While it is native to deny that the Soviet Union and Cuba have contributed to political instability in the developing world, it is equally simplistic to discount domestic political and economic conditions in explaining such instability. Ironically, U.S. supported economic development in the postwar period may have fostered the political unrest that now confronts the administration. The increased literacy rates, urbanization, television and other factors accompanying development have raised the expectations within developing nations with regard to the improvement of economic well being. However, greater inequalities in the distribution of income and wealth and the continued exclusion of newly politicized groups from significant participation in government have characterized modernization in much of the Third World.

UNFORTUNATELY--or perhaps, inevitably, because of its encouragement of rapid economic development--the United States has become associated with the political elites that have fostered inequitable growth. The most notable recipients of U.S. support in recent years have been the Shah of Iran and Ferdinand Marcos in the Philippines. Often, police and military equipment supplied to these and other leaders by the United States to combat Communism have been employed to maintain domestic inequities by political repression.

Until the Carter administration, the United States generally tolerated the violation of human rights in many Third World nations because of their opposition to Communism and the Soviet Union. Carter, on the other hand, recognized the internal stresses in these countries and encouraged rapidly developing nations such as Iran and Nicaragua to open up their political systems.

Reagan's intention to improve relations with the Third World by reducing criticism of human rights violations and re-emphasizing the halting of Soviet expansionism, however, allows these nations to avoid addressing the political and economic inequities that development has generated. While such a strategy may make sense within the short term context of realpolitik, it promises to fail in the long term. Tolerance of repression is deplorable on humanitarian grounds, and it fails in practical terms. As the expectations of the populace rise, the costs of suppressing those demands may exceed the cost of meeting them. The United States, associated with repression by the newly enfranchised, will not be anyone's favorite country.

The U.S. government has probably supported the status quo in the Third World for too long to disassociate itself from political instability and the opportunities for greater Soviet influence in the Third World. For the poorest countries, foreign aid--dispensed by both the United States and international bodies such as the World Bank--is invaluable. For newly industrializing countries such as Brazil, South Korea and Mexico, a reduction of protectionism in the developed world is necessary in order to permit rapid economic growth and the satisfaction of rising expectations.

Reducing the possibilities for political instability and Soviet expansion in the Third World, to a large extent, depends upon U.S> domestic economic policy. If the United States desires stable economic development in the Third World, it may have to supply some of the economic and political flexibility that developing nations lack.