A REVOLUTIONARY WOMAN. By Sheila Fugard. Braziller. 144 pp. $14.95.

IN THIS all too timely novel about South Africa, the year is 1920, the place is an isolated dorp (village) in a semi-desert region, and the tale is told in the first person by Christina Ransome, an Englishwoman who teaches at the coloured school in the dorp's "location" -- the segregated area for non-whites. Why has Christina sought exile in this harsh environment? "I wanted time to think, and I also needed a second chance."

She has enough to think about. Her love affair with Sanjay, an Indian, has left her with searing memories of passion, betrayal and death. Other memories are more nourishing: the fulfillment she experienced in Natal when she took part in Gandhi's campaign of passive resistance. She sees herself as a revolutionary woman, "a follower of Gandhi, and a child of Tolstoy," and clings to the vision of a classless society.

The Calvinist Boers who populate the dorp have their own vision: a righteous society governed by strict standards of racial purity. "We believe that God made the races separate," Petrus Nel, the village leader, tells Christina. "The Coloureds are our servants, and we are their just masters."

It is Nel who informs Christina that she has been dismissed from her teaching post. The reason is community disapproval of her relationship with Ebrahim, the 18-year-old coloured youth she is tutoring for an examination that can help him escape to a freer life. Ebrahim's vision is a fantasy:

"I believe that I came here as a white child, from some foreign land. . . . I was shipwrecked on the coast of Africa, and thrown ashore. . . . The brown people found the casket, and took that beautiful white child and reared me as one of thr own."

The disparate visions collide in crisis when Ebrahim is found to have seduced a 14-year- old retarded Boer girl. Crying rape, the villagers arrest him, but Christina hires a lawyer to plead that what happened was seduction, a lesser offense. She stands bail for Ebrahim, and he is released in her custody to await trial. Once the girl is known to be pregnant, however, the Boers are no longer content to wait for a court to convene. Twelve men form a kommando and pursue the boy to Christina's house. There the conflict reaches its climax.

On this slender limb of a story hang haunting subtexts. Ever present in Christina's consciousness is the troubling enigma of Gandhi's marriage. She feels strongly that the universe must not be ruled solely by men. Why, then, does her wise and saintly mentor not allow his wife a role in his political life? The silent and submissive Kasturbai, Christina recognizes, "reflects all India. Many women reside within her."

ALSO NEAR the surface of Christina's psyche is fascination with "the seductive quality of brown men." While she thinks of Ebrahim as her son, the replacement for the baby she lost by miscarriage, she is also aware that he is "cast in Sanjay's image, with taut thighs, a tongue that is a swimming fish, dark butterfly lashes and . . . olive skin."

Most vivid of all is the recurring image of Lakshmi, Sanjay's child bride. Christina knows that child marriage is an accepted Indian custom, but she deems it "brutal and one-sided," an insult to women. That Sanjay held on to his child bride even while he and Christina were living together struck her as betrayal.

Now Ebrahim has acquired his own child bride, and once again Christina feels betrayed. All she has left is the dream of social justice. She defies the kommando, holding the men at bay on her doorstep:

"We will see a different society. There will be . . . no Boer enclaves and no Coloured locations. I believe that such a classless society is possible in South Africa."

Petrus Nel, who leads the kommando, dismisses her avowal. "You are a woman. We are men and know what is best. This is our land. We have defended it against the Kaffir hordes and the British, and we will repulse any army that threatens us."

This, then, is a novel about apartheid (the term is never used; perhaps it had not yet been coined in 1920), about sexual power and sexual injustice, about a woman's struggle to define herself and her role. Written in a style reminiscent of the kind of high fever in which one drifts in and out of reality, the novel alternates between ritualized formal dialogue and shimmering imagery. Short declarative sentences set up a rhythmic, dirge- like beat as events march to their inexorable culmination. Scenes are deftly captured in a few sentences. Here Christina has walked into the dorp's butcher shop:

"Jan Volschenk is like a berserk king in a Greek play. He raises that meat cleaver, another mad Oedipus swearing at the gods. Lights and livers slither about, as if they possess their own reptilian life, and sausages spill out like human intestines."

A Revolutionary Woman is Sheila Fugard's first book to be published in the United States. Wife of the South African playwright Athol Fugard, to whom the book is dedicated, she is the author of two previous novels. If they are invested with anything like the power and poetry of the present work, their publication here should not be delayed.