While it is difficult to identify precisely the objectives of U.S. policy in Central America, administration statements and their interpretations by the media allow us to form a pretty clear idea of what our leaders are trying to accomplish. The principal long-term objectives seem to be the restoration of peace and order throughout the isthmus, the exclusion of communist influence and weapons wherever found and control of the flow of immigrants from Central America into Mexico and the United States.

To do these things, we are concentrating our attention primarily on the situation in three countries--El Salvador, Nicaragua and Honduras. The first two are the scene of guerrilla insurgencies; Honduras is serving as a base for U.S. support of the Salvadoran army and the anti-communist guerrillas in Nicaragua.

Irked by the charge of over-concentration on military aid, President Reagan of late has been demonstrating a greater interest in political, economic and social conditions in El Salvador, which, unimproved, will tend to nullify the accomplishments of the military programs. In this civil field, the objectives are particularly ill- defined but include intentions to stabilize the ineffective albeit democratic government in El Salvador, to find ways to ameliorate the economic lot of the poverty-stricken majority of the population and to relax the social tensions between classes and regions.

There are many discernible obstacles and threats to the fulfillment of such objectives. Despite current rumors of possible negotiations with local communist leaders, malevolent troublemaking by Cuba and the Soviet Union is clearly a primary threat to U.S. policy. Much the same may be said for the Marxist government in Nicaragua.

But there are many obstacles that would remain even if all communist activities suddenly ceased. Governments in Central America have long been notorious for inefficiency and corruption in the performance of their obligations to their people. It is not surprising that national leaders in key positions are now displaying discouragingly limited ability in using American aid, military and civil, that they receive.

As in most of Latin America, society in Central America is sharply divided between the very poor and the very rich with little or no middle class. Most of the indigent were originally farmers, but by now many have migrated to the cities where they live in suburban shanty towns. The change to an urban environment has brought them little benefit since jobs, already scarce, have been unable to keep pace with the arrivals from the country. Losing hope of a better life, large numbers are constantly moving across frontiers to become transient laborers or unwanted immigrants in neighboring countries; many will eventually add to the illegal immigration into the United States.

These nonmilitary obstacles to American policy have been often discussed by the press in recent months. However, in the heated debate over the merits or demerits of this policy, I have never heard mention of the existence of a seminal cause that is responsible, wholly or in part, for most of the difficulties being encountered by our officials. I refer to the overlooked factor: excess population and its consequences.

Since the warning of Malthus some two centuries ago, demographers, sociologists, ecologists and thoughtful generalists have speculated as to the likely consequences of overpopulations and their future effects on the ecology, human society, national governments and their interrelations in peace and war. Unfortunately, their conclusions over the centuries have had no visible effect on the present-day politicians, diplomats and policy-makers in Washington responsible for our policy in Central America. So it is worth the time to consider how population growth may affect the policy they have adopted.

First, a few demographic data regarding El Salvador, Nicaragua, Honduras and Guatemala. They all have an annual population increase of about 3 percent, which, if sustained, will cause their populations to double in an average time of 22 years (the U.S. growth rate less immigration is .7 percent; its doubling time, 95 years). Their cities will double somewhat faster so that, by the end of the century, each country will have a capital city of over 1 million (Guatemala City will be over 2 million). About 65 percent of the population of these countries is now 24 years of age or younger. The labor force is expected to grow from 7 million in 1980 to 13 million in the year 2000.

What do these figures tell us? First, they remind us that at least until the turn of the century, the present forces and conditions adverse to our objectives in Central America will sharply increase. In the various countries, mounting misery awaits the poor, the result of greater crowding, poverty, hunger, unemployment and ill health. Their hopelessness may be expected to express itself in domestic turbulence, frequent overthrows of government and expanded migration to greener pastures beyond national boundaries.

It is also predictable that many governments, overwhelmed by the mounting burdens of governance will often be replaced by dictatorships of the right or left that will quickly prove equally inadequate to their tasks. If Central America is today an inviting pond to communist fishermen, under the conditions forecast it will offer them a well-stocked lake.

What would happen to American policy under such circumstances? It might succeed to a degree in improving the internal security of countries like El Salvador and Honduras, in neutralizing communist activities such as those now in Nicaragua and in achieving minor improvement in government administration. But the time will never come when we can declare a complete job well done and leave Central America a region of stable prospering democracies.

The hard fact is that unchecked population growth alone creates problems so difficult and so costly to solve that the United States can never afford to take so ambitious a target. It is not merely that the regeneration of Central America is beyond any sum Congress is likely to appropriate for the purpose. We must remember that, concurrently, these same conditions that frustrate us in Central America today are present in virtually every other country in Latin America, many of which, like Mexico, Venezuela and Brazil, are far more important to our national interests than Central America.

This list could be lengthened by adding countries in Asia and Africa which, because of their importance as trading partners, lessors of military bases or formal allies, also deserve a higher national interest rating than Central America. Such funds as we may have for foreign aid, if allocated with due priority, will be exhausted long before the basic needs of Central America can be met.

From these considerations, future Washington policy designers should be able to draw several useful conclusions. They should perceive the folly of considering a genuine Marshall Plan for this part of the world after having appraised the needs of our national interests worldwide and determining priorities in allocating our finite resources. Such an appraisal should lead them to limit our objectives in Central America to something relatively modest, such as the restoration of order in war areas, an end to identified communist troublemaking, and the first steps of a realistic social-economic program in which aid for family planning would be a lead item.

Finally, we might hope that these future policy-makers would henceforth recognize overpopulation as a perennial enemy of our national interests throughout the underdeveloped world and consider it in their global planning.