Humor and acid in new Fugard drama; Master Harold . . . and the boys Play by Athol Fugard. Directed by Mr. Fugard.

In play after searing play, Athol Fugard has dramatized aspects and consequences of the racism (apartheid) that afflicts his native South Africa, oppressing the black man and dehumanizing his white oppressor. The cruel face of discrimination is no less present in Fugard's 16th work, ''Master Harold . . . and the boys,'' now at the Lyceum Theater after receiving its recent world premiere by the Yale Repertory Theater.

But this time there is a difference. ''Master Harold'' rejoices in an abundance of rich human comedy before reaching the outburst of anger that shatters a relationship and climaxes the drama.

''Master Harold'' puts its first foot forward quite literally in a dancing sequence as the graceful Sam (Zakes Mokae) tries to teach his backward fellow waiter, Willie (Danny Glover), the intricacies of the quickstep. It is a wet and windy afternoon outside the St. Georges Park Tea Room at Port Elizabeth. The year is 1950. With the premises deserted, Sam and Willie are practicing for a championship dance contest.

The practice session is interrupted by the arrival of Harold (Lonny Price), nicknamed ''Hally,'' whose lifelong friendship with the two black servants emerges in the easy banter of their discussions of all manner of subjects. From the definition of ''magnitude'' to the game of naming great men, the conversation flows with such naturalness and spontaneity that the allusive associations are almost subliminal.

One of the play's most moving passages is Sam and Hally's recollections of the kite-flying day that followed the pain and humiliation of having to escort the little boy's alcoholic father home from a local bar. In such recollections, Fugard gradually reveals the surrogate paternal role played by the perceptive and devoted Sam. The evidence of this devotion makes Hally's callow, suddenly racist rejection the more terrible.

But Fugard refuses to leave it there. The dance motif that has run through ''Master Harold'' - Hally likens the United Nations to ''a dancing contest for politicians in a world without collisions'' - surfaces again. The conclusion in which Sam and Willie resume their practice offers a tender denouement to a moving play. And since ''Master Harold'' is to a degree biographical, there is some consolation in the fact that the terribly confused Hally eventually matured into the clear-visioned opponent of apartheid, Athol Fugard.

The eloquence and pungent humor of ''Master Harold'' come exhilaratingly alive in the production staged by the playwright. The performance, which runs 105 minutes without intermission, is consistent in both buoyancy and reflectiveness.

Besides his grace, understanding, and kindliness, Mr. Mokae's Sam is a man whose innate dignity helps him regain composure after Master Harold's contemptible effort to humiliate him. For his part, Mr. Price perceives in Hally the insecurity, desperation, and loneliness of a youngster whose still painful relations with his father aggravate the tense crisis through which he is passing. Danny Glover's cheerful second of the two ''boys'' of the title helps enrich Fugard's evocation of a relationship so vital and yet so vulnerable to the pressures inherent in an evil social system.

The modest tearoom designed by Jane Clark can, under David Noling's lighting, seem bleak or cheerful, depending on the mood of the moment. ''Master Harold . . . and the boys'' has been costumed by Sheila McLamb. Wesley Fata devised the all-important quickstep, waltz, and other dance movements.