Will the sanctions approved this week by House-Senate conferees lead to fundamental change in South Africa?

Maybe not. It's important to remember that it is not in America's power to make South Africa do what it is determined not to do. But it is also important to note that the graduated sanctions agreed to by the conferees offer the best chance America has of helping South Africa steer the tricky course between apartheid and revolution. For four years now, that country has learned to count on America's speaking sternly while carrying a limp noodle for a stick.

It will now have to face up to the new reality that America's good will and cooperation no longer come free.

The initial costs, while symbolically important, are relatively cheap. There would be a ban on U.S. bank loans to the South African government (few such loans have been made in recent years), a suspension of nuclear cooperation and a ban on computer sales to South African agencies that implement apartheid as well as a prohibition against the importation of krugerrands, the South African gold coin.

But if nothing in that initial package would hurt South Africa very much, a second phase of sanctions, to kick in in a year unless the president and Congress certify that there has been satisfactory progress toward the dismantling of apartheid, would begin to draw blood. That second phase would ban new private investments and private bank loans (currently running at close to $5 billion) and elimination of most- favored-nation status for South Africa.

The specifics of this week's congressional action, however, are far less important than its seriousness. South Africa is on notice that it can no longer count on the toothless urgings of "constructive engagement," that things will get better between the government and the black majority or else get a lot worse between Washington and Pretoria.

The question South Africa's white minority will have to answer for itself is whether a serious move away from apartheid is a greater danger than the loss of U.S. economic cooperation. In other words, can the government find some way out of its self-imposed mess that still protects the basic interests of whites?

A relatively short time ago, the answer would have been easy: yes.

American activists like to talk of one man, one vote, which South African whites tend to equate with suicide. But there was reason to believe that serious negotiations with South Africa's most highly respected black leaders might have produced a compromise that both white and nonwhites could live with.

The trouble was what the trouble in these situations nearly always turns out to be. Those who hold the preponderance of power are seldom interested in negotiating any of it away -- until they are left without alternatives. And by then, the demands may be uncomfortably high.

The South African government, in a desperate attempt to keep all power in the hands of whites, has undertaken a series of actions -- including the foolish refusal of President P. W. Botha to meet with Bishop Tutu and, more recently, a ban on rallies at funerals -- that seem certain to radicalize even the most moderate black leaders.

The more government officials follow that path, the more likely that blacks will settle for nothing less than one man, one vote, which means that the prospect for a peaceful outcome becomes dimmer and dimmer.

The best hope for now is that South Africa, to avoid the snowballing of economic sanctions, might decide to back off its deadly course and start moving in the direction of racial justice.