It's strange to live in a country where there are still heroes.'' The words seem to echo through this book, which is concerned above all with the nature of commitment and heroism in South Africa. But it is not about romantic hero-worship; it is about the problems, the humanity, the ruthlessness and the cost of political involvement, all against a background of love, squalor or boredom.

It is Miss Gordimer's most political and most moving novel, going to the heart of the racial conflict in South Africa. But it does not deal publicly with riots, tortures or crusades: Its politics come out of its characters, as part of the wholeness of lives that cannot evade them.

The hero of the book, whom we never meet, is Lionel Burger, a respected Afrikaner doctor who joined the Communist Party, worked for the revolution, was jailed and died in prison; and the story is that of his daughter Rosa, brought up under her father's spell, waiting outside prisons and living among dedicated Communists, yet trying to escape, alone, after her father's death, from a commitment that was all-enveloping.

For Burger was the kind of South African Communist who was drawn to the party by his humanity and determination to share the cause of the blacks; and in his house blacks and whites came together with a sense of common hope and faith in the future, defying the apartheid surrounding them. With his Afrikaner ancestry and his political understanding, Burger was a man who, as a compatriot describes him, ''could have been a prime minister if he hadn't been a traitor.'' (His story bears some resemblance to the actual story of Bram Fischer, the distinguished Afrikaner lawyer who likewise became a Communist revolutionary and died in jail.)

What is it like to grow up in the shadow of someone so dedicated and so charismatic and then to seek to become a separate, fulfilled individual? Rosa's answer, as it unfolds, tells us not only about South Africa but about the whole nature of commitment. It was Burger's gift to be able to break through ''the closed circuit of self,'' to give purpose to other people's lives; in his house the real definition of loneliness was to live without social responsibility.

The opening chapters describe vividly the splendors and miseries of that commitment; the passionate concern with the future, the moral certainties, the sense of identification with blackness as a way of perceiving sensual redemption, revealed in the magnetic attraction of the beautiful Marisa Kgosana. But on the other hand, there is the bossy narrowness of other white Communists, the jargon of dogma, the lack of escape and the sheer brutalizing effect of the race conflict. When Rosa sees an old black man senselessly flogging a donkey in Soweto, yet cannot intervene, she realizes suddenly ''I must know somewhere else.'' She makes her bid to escape, flying off to the South of France to stay with her father's first wife, in a world of gigolos, lesbians and sun-seekers.

It is a spectacular transition, showing the brittle sophistication and lushness of this cosmopolitan life through the eyes of a South African girl, ''dissolving in the wine and pleasure of scents, sights and sounds existing only in themselves, associated with nothing and nobody. . . .'' The style itself becomes sensuous and multicolored, against the stark background of the Johannesburg past, as Rosa loses herself in the laziness and the waveless peacock-shaded sea.

She falls in love with a French teacher, stays in London and Paris, and finds a new dimension in her love affair that seems to put politics in a neat theoretical pigeonhole. The tolerance, the detachment and cultivation of Europe surround her: To the lesbians in the South of France, the police are no closer than the crime thrillers on television.

Yet the responsibility, the need for identity, remains. The denouement of the novel is too subtle and important to be summarized, for it is about much more than the need for a political cause; it is a whole view of individualism. In her father's house the people had discovered their own kind of individualism, with the liberation that comes from belonging. Her black childhood friend, in spite of her guilt and his bitterness, was still a blood-brother. The political attitudes came from the inside outward: ''It was a human conspiracy, above all other kinds.'' Rosa sees clearly enough the limitations of that conspiracy--the exploitation, the psychological blackmail and the ultimate cost to herself. But she is still Burger's daughter.

It is the combination of political authenticity with sensuous awareness that makes this novel so powerful. Its account of black movements, against the historical background of real people, is harshly realistic; the intense argument in a house in Soweto has the sharp detail of a documentary.

No one has better described the vigor and humor, as well as the misery, of Soweto. Yet the political moments are always illuminated by the intense observation of people and places--tiny details precisely and lovingly described--that brings every incident to life and that give Miss Gordimer's writing such universality. People, landscapes and politics are blended together in this evocative style, and through the eyes of the young, bewildered daughter the wide arc of South African politics comes into sudden focus. It is an integration reminiscent of the great Russian prerevolutionary novels.

It remains extraordinary that such a novel should come out of a country so uncompromising and so increasingly brutalized, where the image of the flogged donkey has such fearful relevance; and it might seem equally surprising that an author of such sensitivity could live there. But this, too, was a Russian phenomenon. The very bleakness of the political predicament and the closeness to suffering seem able not only to provide insights into the political crisis, but to give a heightened awareness of the richness and values of lie.

In one passage the author describes how Rosa and her father's first wife find themselves subtly transformed for each other by their relationship with Lionel Burger, ''like a change of light transforming the aspect of a landscape.'' Coming out of the harshness of South Africa, this dazzling book also brings a new light to the landscape, not only of Johannesburg and its black townships, but of the European cities that have forgotten about darkness