We should not make the mistake of believing that all white South Africans support apartheid. It is a fact that a minority of South Africans who are white oppress a majority who are black, but the issue is not black and white, it is gray and complex.

Indeed, a tiny but significant minority of whites oppose their government's practices and work on the side of the resistance. The Progressive Federal Party pushes within Parliament for black enfranchisement. Trade unionist Neil Aggett was killed while in police detention. Several whites have been arrested along with more than 1,000 blacks during the current state of emergency.

One of the oldest white protest organizations is the Black Sash, a 30-year-old women's group with 1,500 members that was formed when protest was still permitted. Under the current protest ban, one woman standing alone with her poster, out of sight of the next person, constitutes a demonstration. Last week, I spent an hour with Black Sash leader, Sheena Duncan, who was in Washington lashing out at President Reagan's support of her government.

Because she believes outside pressure is the only hope for change, Duncan supports economic sanctions against her now economically vulnerable government.

"We believe that pressure from the Western democracies is of the utmost importance in ending apartheid," she said. "I can't make out why Reagan backs constructive engagement. Sometimes I don't believe they understand . . . . Other times I fear U.S. policy is less about apartheid than a world view that puts capitalism on one side and communism on the other so there is nothing in between."

Although her group is not anticapitalist, Duncan says capitalism's support of apartheid has backfired. "Black South Africans identify capitalism with the political system and say, if this is capitalism, we want nothing to do with it. So if the U.S. is afraid of Russia, your policy is driving people toward them. Americans used to be a model of what we thought justice was. Now people are anti-American. I don't like to see America become the number one hated government in the world."

The wife of an architect and the mother of two daughters, Duncan's understanding and vision of what the political system means to blacks comes from working in the Black Sash's advice offices. "We play a limited, supporting role to blacks. We never go to a community, but we wait for them to ask us. If, for example, a community is being removed to a homeland, they may ask us to help set up a press conference. People ask for help with all sorts of problems."

But when it comes to dealing with fellow whites, the Sash is more aggressive. "We try to be a catalyst by explaining to white South Africans what apartheid really means, to show them that civil war is inevitable on the current path."

Apartheid, a policy designed to exclude the 72 percent black population from participating in the common society, rests on three main pillars: the physical removal of most blacks from their homes to "homelands" situated on less than 14 percent of the land; a system of passes and laws designed to keep blacks from moving into white cities and towns, and a political apparatus that has effectively taken away the citizenship of millions of blacks.

Now, the government is talking negotiation, but black leaders are demanding that concrete steps to dismantle apartheid be made as a declaration of intent. Says Duncan: "Black history has been one of patient willingness to negotiate, but talking always proved to be a trap. They were not negotiations but talks designed to manipulate blacks into immobility."

Now even Duncan is amazed at blacks' determination to be free. "It's extraordinary to see young people jeering at police in armored cars. There is a total feeling that their resistance is not going to be crushed. In just three days, the consumer boycott in Port Elizabeth was so effective that businssmen were yelling."

Duncan thinks the Sash has escaped being banned because it is an organization of women. "We're immune because we're unequal."

But they are determined to keep fighting the system. "Just as the visibility of Bishop [Desmond] Tutu . . . gives him greater protection, being white gives us more protection. But that in turn gives us greater responsibility."