Talent and conviction; Ah, But Your Land Is Beautiful, by Alan Paton. New York: Charles Scribner's Sons. 192 pp. $12.95.

Ah, but your land is beautiful. It's what a tourist can honestly say to South Africans in preference to dwelling on the chill of racial injustice in the air. The land is beautiful, as you drive past the rich fields, soaring mountains , and glorious shores. You try to remember the beauty when you stop for gasoline out in the country and find the small sandwich shop open to white customers only; when you see the hostel for thousands of black workers whose families are not allowed to live with them. The heart-lifting thing about Alan Paton is that, even after almost eight decades of immersion in this self-sundered land, he does remember the beauty - not only of the place but of the people, those who have patiently borne injustice, peacefully resisted it, or thoughtfully begun to refrain from imposing it.

Paton knows full well the ironies in the title of ''Ah, But Your Land Is Beautiful,'' whether referring to a tourist's polite evasion, to the land expropriated from black people, to the shattered dreams of an Afrikaner official entrapped under one of his own government's draconian laws. Yet Paton goes beyond irony in this novel - only the second since his classic ''Cry, the Beloved Country'' of 35 years ago - to evoke the redeeming individual possibilities that any country must value. A final inkling of redemption touches even the sender of graphically obscene letters to a white teacher who takes a leading role in the nonracist Liberal Party - the latter character recalling in some respects Paton's own experience in the 1950s of which he writes.

Sometimes, amid a range of harsh to humorous voices, the prose echoes the biblical cadences of ''Cry, the Beloved Country.'' A remarkable climactic scene centers on a church ceremony patterned on the washing of the feet by which Jesus displayed such humility and love toward his disciples. There are agonizings by both black and white Christians over the rules prohibiting them from worshiping together.

But this book does not have the first novel's parablelike narrative simplicity. Pausing for only a few passages of expository connecting tissue, it plunges into self-contained dialogue, letters, clippings. It lets the reader participate in figuring out what is happening. Links between events gradually get formed.

Sometimes the mechanics become a bit obvious, as in the way a young Afrikaner bureaucrat's letters to his aunt inform us of her end of the correspondence. He may come off as impossibly fatuous in idealizing separate development of the races as the road to a golden age. Yet the device permits the humanity of the young man to emerge, while the greater humanity of the aunt shines through sooner.

Perhaps some character detail is sacrificed for representing various points of view. But as white, black, Indian, and mixed-race South Africans pass through these pages, they convey the blighting effects of injustice on both the rulers and the ruled.

Paton is deadly in the dark comedy of hair-splitting legalities bestowed on basically unjust laws. But he also shows a junior officer trying to ameliorate the severity of a senior officer. A judge refuses to tolerate casual abuse of a black man. Individuals of all hues risk their futures to take small or large stands for what they have come to see as right.

Then they face the decisions on how far they can risk their children's futures, too; the necessities of protecting their impulses from political subversion. And there is the counterpoint of young love, husband-and-wife raillery, references to Albert Luthuli, Trevor Huddleston, and other figures in the news during those years.

Paton here is exercising his talent and conviction on South Africa in the 1950s. But he could be writing about today in the sense that most places, like his beautiful land, still have need in one degree or another to see and release the beauty in each of their people.