The U.S. civil rights revolution started, as these things often do, with an economic boycott -- of the bus system in Montgomery, Ala., in 1955. Five years later, the movement was reinvigorated when four black college students nonchalantly walked into a Greensboro, N.C., Woolworth's, sat down at the whites-only lunch counter, and refused to leave until they were served. If there was any doubt that the sit-in was a boycott by another name, Woolworth's settled the matter. By the end of the week, it had closed its store.

All that, as they say, is history -- a history President Reagan misread when he conscripted the American civil rights revolution to defend his position on South Africa. ''Our own experience teaches us that racial progress comes swiftest and easiest, not during economic depression, but in times of prosperity and growth,'' the president said in arguing against sanctions that would weaken the South African economy. But our own experience teaches just the opposite. It is precisely when economic interests are threatened that progress occurs.

The correlation that the president alleges simply isn't there. In our own country, the prosperous 1950s did not produce major civil rights breakthroughs. Those came later. And in South Africa, the incredible boom years of the 1960s and the continuing prosperity of the 1970s did not see a concurrent loosing of the racial laws. As long as the white community remained prosperous, it had no reason to change matters.

The president's thesis is hardly new. Back during the South Africa boom, it was widely believed that a rampaging economy (real growth averaged 7 percent a year) would make apartheid unworkable. Foreign firms -- many American -- were entreated to enter the South Africa market with the promise that the human-rights situation would improve. Prosperity would compensate whites for the loss of racial privilege -- turn them from hard Boers into pragmatic, liberal businessmen. Why, the need for skilled workers alone would bring down the racial laws.

No such thing happened. Instead, the racial threshold was raised. If the mines demanded more workers than the white community could provide, then blacks were brought in -- but skilled jobs, such as blasters who work with explosives, were limited to whites. Throughout the economy, that principle was applied.

One goal of economic sanctions is to bring pressure on the white business community so that it, in turn, will pressure the government for reform. Already, that is happening. Nothing so shocked the business community as the refusal of American banks to continue lending to South Africa, the subsequent decline of the rand and the wrenching sound of American firms pulling up stakes. It was no coincidence that after the rand fell, some of Johannesburg's business elite flew off to Lusaka, Zambia, to meet with leaders of the outlawed African National Congress.

In a speech delivered to a White House claque that applauded a reference to anticommunism but not to human rights, the president used economics and history to justify a policy based mostly on conventional anticommunism. He got it all wrong. If necessity is the mother of invention, then adversity is the mother of reform. Our own civil rights era is instructive. When it comes to South Africa, the calls have gone out. It's time for a boycott.