"When NBC showed pictures of the starving masses in Ethiopia," Rep. Bill Gray said, "America changed its foreign policy. People asked: Why are we not doing something about that? The funds went up from $12 million to $107 million."

This is the model shining before many of those who hope that the new demonstrations against apartheid will create a popular awareness of the iniquities of the system in South Africa and then a popular demand for change. "If people understood what apartheid is," Gray told me, "they would want it changed." The aim is to render the Reagan administration's policy of "constructive engagement" politically untenable and to bring a tougher American policy to bear.

The demonstrations mark a late but expectable chapter in the story of lack political assertiveness in 1984. In the political campaign, there never really was a foreign policy chapter, in part perhaps because black presidential candidate Jesse Jackson had chosen to identify himself most conspicuously, in international terms, with the Palestinian issue, and lacked plausibility as a spokesman for blacks on South Africa.

There was a vacuum in black commitment to an international issue -- and an untapped white readiness to respect such a commitment. Del. Walter Fauntroy, TransAfrica's Randall Robinson and others came along to fill it.

Then there is the Tutu factor: the Nobel Peace Prize given recently to Bishop Desmond Tutu of South Africa greatly broadened the attentive American audience. The bishop is the ideal person to tell Americans of apartheid: a victim but a survivor, moral without being threatening, universalist in his message, winning in his manner. He happened to be present in this country as the demonstrations began, and he has helped immeasurably to establish the issue on a moral plane.

When all this is added up soberly, however, the prospects for early change do not seem to me bright.

To start with the most important thing, Gray is surely right when he says that the mass of Americans have only a slight awareness of apartheid. But there are two key aspects of apartheid of which little generally is known. One, the aspect that the new demonstrations can publicize, is its horror and moral monstrosity. The other is the strength, beyond tenacity, with which the white minority enforces its hold.

The use of some of the tactics and imagery of the American civil rights movement conveys the impression that, in South Africa as in this country 20 years ago, the protesters can reach out to a waiting sympathetic public and to a body of supporting tradition and law in order to remedy injustice. But this is terribly misleading. Imagine that opponents of equal rights in the American South could have summonedthe full armed power of a Soviet-type central government in Washington in their behalf. No strategy for stirring change in South Africa can go far without taking this grim reality into account.

The administration's strategy of "constructive engagement" has some grave disabilities. To many of those who feel most strongly about apartheid, it has the appearance of unfeeling and even immoral collaboration with the enemy. It exposes the United States to charges, made in the international arena as well as at home, that it gives aid and comfort to a pariah regime. Its processes are admittedly slow and its measurable results tentative and small.

Constructive engagement also suffers from being widely seen as the private construct of a single middle-level official, Chester Crocker, head of the State Department's Africa bureau, who has won respect for his personal seriousness even from many of his critics, but who is often put down as front man for a policy that Ronald Reagan upholds for considerations of expediency.

The policy, however, does have a core of realism: it acknowledges and attempts to address in its fashion the immense power that the white minority can mobilize behind its resistance to change.

A telling question then arises, as Rep. Stephen Solarz points out. Solarz cosponsored with Gray the mild economic sanctions that the last Congress turned down. How can the administration's quiet words and small pushes alter a system so deeply and powerfully rooted? Whatever its promise, doesn't constructive engagement deliver us the worst of both worlds -- moral and political obloquy without the compensation of real change?

In short, the latest burst of attention to South Africa takes us all to a place where we have to think harder about the uses and limits of American power. "Doesn't constructive engagement deliver us the worst of both worlds -- moral and political obloquy without the compensation ofreal change.

In short, the latest burst of attention to South Africa takes us all to a place where we have to think harder about the uses and limits of American power.