When the Rev. Allan Boesak speaks of the children of South Africa, his expressive face hardens and his voice stumbles into anger.

"They grow up with the smell of tear gas," says the outspoken South African critic of apartheid, who is also the father of four young children.

"They grow up in the violence of apartheid. They have seen their little friends shot down next to them in the street. They go to church, and like their parents, have to run for cover as we come out of worship. By the age of 4 or 5, they sing all these freedom songs and have their fists in the air and get excited when I get there.

"In a sense, some people feel proud our children are so politically aware. I have a sense when you are a child, you should be a child. What do you do in 15 years with a person that has been raised on violence? What is being destroyed in the souls of our children?"

Boesak, 40, the founder of the United Democratic Front, the main nonwhite activist organization in South Africa, and a minister in the Colored branch of the Dutch Reformed Mission Church, must worry about both the souls and the upraised fists. With antiapartheid political leaders jailed or in exile, Boesak, along with Anglican Bishop Desmond Tutu, has been drawn from the pulpit to the streets, his ministry bringing him before the guns of the South African police and behind the bars of South African prisons.

"If there is a situation in the world today which justifies armed rebellion by the people, it's South Africa," he says. "But you will not hear me say that easily. In the midst of all this, someone's got to be sane enough to remind people of what violence really does. Someone's got to be sane enough to hold onto visions of the things that truly make for peace."

Until several weeks ago, it was not clear whether Boesak would be allowed to leave the country to speak at last Saturday's dinner at the Washington Hilton for the African and Caribbean issues lobbying group TransAfrica, but he was finally granted a passport and came with his wife Dorothy to the United States. He sits now in his hotel suite, worrying over the good barber no one seems to be able to find.

"In this hotel they only know how to cut white people's hair," he laughingly complains to TransAfrica Executive Director Randall Robinson. "When I was in Atlanta, Andy took me to his."

A Hilton staff member quickly promises the barber would be found.

There is also talk of Concorde flights to Europe and connections to Johannesburg, and the possibility of a quick trip to Las Vegas because "my children have told me not to come home without an autograph from Bill Cosby."

Cosby called Boesak's family during the activist's recent incarceration. The four Boesak children, already Cosby fans, were thrilled.

"That was so great," says the father. "They were heroes in school for weeks, because it was in the papers: 'Cosby Calls Boesak Family.' "

Boesak is a small, trim man who sparkles when he talks about his children and whose solemn phrases about South Africa are punctuated with humor.

Asked when South Africa will achieve majority rule, he refuses to give a date: "I always leave those projections to my friend Bishop Tutu -- bishops are a lot closer to heaven." Speaking of Afrikaner internal dissension in his speech to TransAfrica, he roars, "What are they fighting about? Nothing that matters to you or me!" and with a giggle and then a guffaw, slips out of his oratorical furor and into the audience's laughter.

But the humor is only a momentary relief. Boesak is currently awaiting trial on charges of "subversion" for speaking in favor of school and economic boycotts and planning a march last spring to the prison where African National Congress leader Nelson Mandela is held.

June 16 is the 10th anniversary of the Soweto uprisings in which hundreds of blacks were killed. The government has banned public meetings marking the anniversary, but Boesak says he and others will resist. They will hold church services, they will march, they will defy the government bans.

And there will be, he says in the pragmatic tones of a man speaking about a certainty, "a bloodbath" on that day. For a man who describes himself as "the spiritual child of Martin King and Gandhi," this is a painful forecast.

"Violence destroys something in you," Boesak says. "There is an element of uncontrollability in it. People say I sound like a hopeless romantic in the South African situation. Maybe they're right. But . . . the people who say violence will solve all problems, the total militarization of Reagan in this country -- I think that is romantic, that by grabbing the gun and eliminating the enemy you solve the problem.

"I say to my people, 'If we begin to put our faith in violence this way, don't you fool yourself, this is going to happen to us. Before you know it, the desire for violence, the lust for violence, the naturalness of violence, overcomes you. You never control it, it controls you.' In western society it's the Rambos of the world who are the heroes. I think that's sick. It twists our values beyond almost any recognition of humanity."

Both of Boesak's parents were classified Colored (of mixed race). When he was 6, his schoolteacher father died, and his mother became a seamstress to support her eight children. She still tells stories of her second youngest son's precocious calling, stories that embarrass him. "I would force the family to sit down and listen to what I thought would be a great sermon," he says with a smile. "I would get my sister and her dolls in the garage to listen when I was 4 and 5."

At 17 he entered the university and seminary and was ordained at 22. In the intervening years he considered leaving the Dutch Reformed Church, the denomination of most Afrikaners, the church that had for generations espoused and given moral underpinnings to apartheid and which in 1857 established a separate branch for nonwhites that leaders of the "mother" church referred to as the "daughter."

"You can just imagine that paternalistic thing," Boesak says, smiling again, this time more ruefully. "I call it ecclesiastical colonialism. It was totally inadequate. All of my teachers were white. One of my early frustrations was dealing with the attitude of those people."

But with the encouragement of a like-minded white Dutch Reformed minister, he stayed in the church. He studied in the United States at Union Theological Seminary in New York and in the Netherlands. Over the years, he worked from within the church, winning a great victory in 1982 when the World Alliance of Reformed Churches declared apartheid to be a "sin" and "heresy."

"That finally took away all moral pretense, the moral and religious base of the system," he says of the Alliance's declaration. "All that exists, and you can see it every day, is naked greed and power and the violence without which apartheid cannot exist. There is no self-respecting minister in the white Dutch Reformed Church who can now preach that apartheid is the will of God."

Pretoria has retaliated. Last year a South African newspaper reported that the government was running a smear campaign against Boesak, spreading tapes of a supposed "bedroom scene" between the married Boesak and a young, white church employe. The Johannesburg Star also said its reporting showed the stories to be true. Boesak denied the charges, but was suspended from his ministry while a church commission studied the case, which was seen as a serious moral question in the Calvinist community. Boesak later said he was having a "relationship" with the woman, but described it as "unique" and innocent. Without revealing the process by which it reached its decision, the church exonerated Boesak and reinstated him.

South African editors say they are periodically offered "exclusive" stories about antiapartheid leaders by the national security forces, which they refuse to publish, and the incident spurred discussion and condemnation of the government's tactics.

"It was a smear campaign that failed miserably," Boesak says. "They actually thought it was going to be the end. My family was wonderful during all of that. It was not easy for them, to put it very, very mildly. But in the end [the security forces] were defeated, and we are now stronger than we have ever been personally and otherwise."

Boesak speaks about the South African regime as if it has already begun its fall. It is inevitable, he says, that Mandela will be freed. Each new repressive law is only one more sign of the government's terror and recognition of its own impending death. Despite the talk of bloodbaths, despite the despair, the man who calls himself a "dreamer" often sounds buoyant, elated.

"What I want to do, what I try to do with my own children and the kids in my parish, is to make them understand that fighting for justice and dreaming about justice ought to belong together. Because if you lose the softness of the dream about justice and humanity and the things that really make for peace, you become so bitter that nothing matters anymore.

"They don't know what humanity is," he says of white South Africans. "They don't know what it feels like to be truly joyous . . . they are far too neurotic about their future because they are so guilty about their past. I say to my people, 'The one thing we have to do is keep on singing.' "

Later that evening, Boesak speaks to the crowd of 1,500.

"Soweto is more than a name. Soweto is the condition of South Africa," he tells them.

"Since Soweto in 1976, we have gone from funeral to funeral to funeral. Since Soweto, we have lost all innocence in regard to the South African government and its intentions. Since Soweto, we have been bereft of all illusions we may have had of the willingness of the government to use every force at its disposal to maintain its position of power and privilege . . . "

And the crowd is on its feet.

On June 15 Boesak will preach to his Cape Town parish from II Samuel. In the quiet of his Washington hotel room he says he will tell them the story of Rizpah the Israelite, whose two sons King David killed as sacrifices to appease the Gibeonites. Rizpah's sons were hanged on a hill and left there to rot.

"And Rizpah the daughter of Aiah took sackcloth," the Bible says, "and spread it for her upon the rock, from the beginning of harvest until water dropped upon them out of heaven, and suffered neither the birds of the air to rest on them by day, nor the beasts of the field by night."

"She would not allow them to devour the bodies of her children," says Boesak. "I think what we are called to do right now is have that kind of courage. Our children are there. They are the sacrifices on the altar of this Molech which apartheid has become. The government doesn't care. It kills our children and their bodies lie on the street almost literally. We cannot bury our dead in peace. The funeral procession is broken up by police with guns and tear gas and our people have to flee while the coffins are strewn across the street.

"What we need now are people with the courage of Rizpah. King David thought it was all over. By sitting there she refused to allow the king to forget what he had done. In the end, he goes up on that hill and he takes those bodies and he buries them and he gives them full honor. There is power in that story for South Africa."