UNLESS YOU ARE a close follower of the United Nations, you probably are not familiar with the name of H. Carl McCall, the United States alternate representative to that august international body for "special political affairs."

I must confess that I had never heard of Ambassador McCall until I met him recently in Hawaii, where he was giving a speech on Third World problems to an unlikely audience -- a convention of food editors.

I have no doubt that we'll hear more of and from McCall, a handsome young black man from Boston's Roxbury ghetto. For five years prior to going to the United Nations early in 1980, he represented Harlem in the New York state legislature.

An ordained minister (United Church of Christ) as well, McCall does the best job this side of Andrew Young of articulating the identity of black America with the struggle for economic justice by the poor nations of the world.

What interested me particularly was that McCall was willing to take positions in a public speech that go far beyond the cautious posture of the State Department on economic negotiations with the Third World countries.

In the view of the United States -- represented by Secretary of State Muskie -- and of other rich nations, the Third World's demands for "a new economic order" are simply excessive.

But most Third World nations believe they are still treated as colonies for the benefit of the rich world. In McCall's words, they feel that poor peoples' needs "are too often bypassed in the pursuit of profit, convenience, comfort and power (by the rich)."

JUST LAST WEEK, the U.N. General Assembly, which had called a special session to resume the "North-South" dialogue on how to increase aid to the poor, fell on its collective face. In a bitter mood, the rich and poor couldn't even agree on an agenda for continuing the discussions.

In Washington at the end of this month, the same problems are going to come up at the annual joint meetings of the World Bank and the International Monetary Fund. And something of the same result is likely.

"There will be a lot of talk, but almost no action," says a high IMF official sadly.

This is somewhat ironic, for one of the contentious issues that has come between the rich and the poor is the very structure of aid to the poor, much of which is funneled through the bank and IMF. These organizations -- especially the IMF -- are regarded by the Third World as pawns of the rich nations. The poor would like to see most of the aid and loan functions transferred to the United Nations itself, where they have more clout.

State and Treasury Department officials insist that the Third World nations are indulging in a delusion. They fail to concede how far both the bank and IMF have gone in adjusting themselves to the current, real needs of poor nations, Carter aides say.

"They have been tragically misguided in New York," said Assistant Treasury Secretary C. Fred Bergsten. "These [the IMF and the bank] are the institutions doing the most for those guys, and they [the Third World] are jeopardizing their very existence."

McCall, as if directing his words to his State Department employers, argued in his Hawaii speech that the United States must reach out to the Third World and try to satisfy its needs.

"Many Americans view the Third World demands . . . as yet another anti-American, anti-Western, anticapitalist harangue, on the same order of the rhetoric used by Fidel Castro in addressing the U.N. General Assembly last fall," he said. "Those who view (this) dialogue in such a light also tend to view the United Nations itself as a sounding board for anti-American sentiments on the part of the Third World majority."

THE UNITED STATES may be the largest donor of foreign aid in dollar terms, McCall concedes, but he is quick to point out that the United States ranks only 13th out of the 17 major industrial nations in development giving on a per capita basis.

For too long, McCall said, the rich world has called the tune, implying that the North has exploited the Third World's raw material resources while pushing its sales of manufactured products.

"It is little wonder that they want to change the rules, McCall said, urging adoption of reforms recommended by the Brandt Commission -- reforms that the Carter administration has effectively shelved.

McCall's no-holds-barred appraisal has one significant omission -- the same that tilts most U.N. discussions on Third World problems. He fails to mention the responsibility of OPEC, which by raising the price of oil from less than $2 a barrel to more than $30 a barrel in this decade has caused pain and suffering for poor and rich nations alike.

To be sure, OPEC is not the only cause of Third World problems, but there is a conspiracy of silence on this issue among many well-motivated men, including McCall.

The interdependent world of which McCall speaks eloquently faces diminishing economic growth -- and rising Third World population -- in the '80s. That spells real trouble, and neither poor nor rich nations can close their eyes to the fact that much of the resolution of the problem is in OPEC's hands.