Zakes Mokae, black South African, in play about apartheid; also 'Agnes'

Toward the end of Athol Fugard's ''Master Harold . . . and the Boys'' (at the Wilbur through Nov. 20), a young white man spits in the face of his older black servant, Sam, who has raised him and given him more fathering than his own father ever dreamed of.

It is an overwhelming moment in a gripping play.

All the more poignant, then, to sit in a basement restaurant across the table from Zakes Mokae, who plays Sam, and to look into that broad face with all its record of pain and life and joy and all the other things that make us human. And to hear him talk for an hour about his views of apartheid, his friendship with Fugard, the recent hanging of his brother in South Africa, and the multilevel meanings of this remarkable play.

With ''Master Harold,'' Fugard has created perhaps his quintessential masterpiece. The play is openly autobiographical, and it has its real-life counterparts for Mokae. It is also widely considered one of the best plays of our time, one that chronicles the life and culture that Mokae has known for as long as he can remember.

The play revolves around an afternoon in the lives of three people, Willie, his fellow servant Sam, and young Hally (Master Harold.) It starts as a simple dialogue between the two servants about a dance contest coming up, and it waltzes you engagingly around the floor.

But, as Mokae points out, ''Before you know it, you are in the middle of something.

''It's really such a simple play. Just these two guys talking about the dancing contest. And this relationship with the young boy Hally. But underneath, there is all this stuff.'' He makes a large churning motion with his hand.

He is a quiet man with large eyes filled with dark questions, eyes that roam endlessly about the room, as he talks. Suddenly he will erupt with laughter, and then the eyes sparkle and dance, as when he says, ''I try to have fun when I work. You have fun acting in this play. But you can also say it's a lot of pain, too. You don't have an intermission; and you have to stay on top of things. And you can't be lax about anything.''

Mokae opened the play in New Haven, Conn., before the decision had been made to bring it to New York. He then went on to win a Tony for his performance on Broadway, after which he got into a dispute with the management over money and left for a year.

He then returned to South Africa, just in time to visit his brother a few times in prison before he was hanged, Mokae says, for robbery. During that time, he adds, he saw his mother and father in Soweto, a couple of miles from Johannesburg. His father passed on three days after his brother was executed. His other brother was involved in school riots in 1976 and has been unemployed ever since.

The blacks in that area live in ''houses that are all alike; they look like little gray boxes. The streetlights don't work. The garbage is infrequently picked up. Water gets turned off at anyone's whim. It's hard to explain it.''

The producers called Mokae a few weeks ago, when James Earl Jones, who had been playing the part ever since, was too ill to go on.

So he is back at work on a Fugard play, something he has been doing off and on ever since Fugard started writing plays. He and the playwright met in South Africa. Mokae was a musician, and Fugard was a beginning writer.

That was in the late '50s. Since then, Mokae has opened almost every play the white South African playwright has written.

''We don't even think in terms of 'friends,' '' he says. ''It's more like he is my brother. I call him my playwright. Which is very nice. How many actors have a playwright?''

Master Zakes . . . and the playwright?

He laughs louder, a rich, loamy laughter, relishing the thought, and repeating a couple of times, ''Master Zakes . . . and the playwright. Yeah, that's good.'' It is a personal moment when the message of the play makes connection with his life. There are many such moments during the interview.

''I have known characters like Sam. I have known Willies, too. And the Hallys , you see them day in and day out in southern Africa. They spend the whole night telling jokes about 'niggers.' '' He says that such jokes are frequently told in the presence of black servants.

''It happens all the time in South Africa. The fact that someone is born with a lighter skin than you means they are better than you, means they are entitled to everything.

''I have traveled, so I can talk about it without screaming. But that doesn't mean I don't get mad.''

He thinks racism will be with us for a long time - and not only in South Africa. ''You have the die-hards everywhere,'' he says, suddenly laughing. ''There are some people, no matter how nice you are to them, they will say, 'I don't care. You are black, and I will die hating you.' ''

Things are not so simple and clear-cut in ''Master Harold.'' Here we are dealing with a boy whose love for a black man is poisoned by a pervasive hatred he only halfway understands.

Characteristically, Fugard doesn't leave us with either the hate or the love, but with a hope poised precariously somewhere in the middle. It's this hope that leaves you so stunned and wondering.

''Some people come backstage after the play. They don't say anything. They look at you. They want to say 'thank you,' but the words . . . I mean . . . really, they are saying something more than 'thank you.' '' From a Boston Arts contributor:

The Shubert marquee of ''Agnes of God'' (running through Sunday) reads: ''Murder was the least of the sins she committed that night.''

Ignore it - it's a titillating, and false, come-on.

For those who didn't see the show during its popular pre-Broadway run two years ago, ''Agnes of God'' deals with some pretty weighty material. It's a psychological thriller that descends, layer by layer, into the past and motives of an amnesiac young nun accused of murdering her minutes-old child - and into her relationships with her mysteriously overprotective mother superior and the doctor assigned to determine the nun's sanity.

Everyone's secrets get revealed. What you end up with is a nose-to-nose battle for the soul of the young nun, a showdown between the ''heart'' of religion and the ''head'' of medicine. Neither ends up unsullied.

The show is not all gloomy, however. It's lightened considerably by one-liners between Mercedes McCambridge (superb as the hearty but anxious mother superior) and Elizabeth Ashley (funny but mannered and superficial as the chain-smoking, atheistic doctor).

The real heart of the evening, however, belongs to Maryann Plunkett as Agnes, who hovers between the refuge of adolescence and her terror of adult responsibility. It is a moving performance. Catherine Foster