KENNETH KAUNDA has always been regarded as one of the "good" leaders of black Africa. During the Nigerian civil war he came out in support of the Biafrans, on humanitarian grounds. He is more ready than most of his fellow-presidents on the continent to condemn tyrants, such as Idi Amin of Uganda (although it must be said that Zambia's head of state keeps fairly quiet about the notorious doings of his northern neighbor, President Mobutu Sese Seko of Zaire).

This book merits attention, because in it President Kaunda is plainly bracing himself for what he fears will be "a long, hard struggle which cannot exclude the use of force" against white rule in South Africa. Admittedly, much of the text is a slog; there is a great deal of pulpit language -- inevitable, perhaps, given Kaunda's own missionary upbringing and the fact that his thoughts have been assembled for him by Rev. Colin Morris, a Methodist media man.

Yet the timely message comes through in the last 40 pages. "Dr." Kaunda (Fordham University gave him an honorary doctorate of laws in 1963) is one of the most gentle spokesmen for independent Africa, yet he does not waver in his devotion to smashing apartheid. Just as the Afrikaners see themselves as standing firm in the name of God, the Zambian leader regards himself as a crusader against racism's powers of darkness. There can be no coexistence.

The triumph of the guerillas in Zimbabwe (formerly Rhodesia) has set a pattern for the final round. As Kaunda says: I ended up supporting armed struggle in Zimbabwe because I could no longer believe that anything is preferable to the use of force." As this implies, his stance changed gradually, after the rebellion against British rule by Prime Minister Ian Smith in 1965. At first, Kaunda told his army to keep the exiled black nationalists from Rhodesia on a tight leash. Sorties from Zambia were hindered and military equipment confiscated.

Was he converted to violence merely because it seemed more feasible when the Portuguese had abandoned Mozambique and a second front against Rhodesia could be opened up? That may be too cynical -- but as Kaunda admits, he had never opposed the use of "a limited degree of force" by Britian to put down Smith's rebellion. He is no pacifist.

Indeed, it was an upsurge of "spontaneous" violence by his followers in Zambia's northern provinces in 1961 which forced constitutional changes, opening the way to self-government, then full independence. Yet Kaunda never advocated the violence publicly, since that would have earned him another spell in jail. He always took care to talk more in sorrow than in anger. Looking back, he says, his nonviolence was "an exercise in public relations."

But that public relations phase has long been passed in South Africa. Everyone knows just what the issues are. Kaunda ends by appealing to the West's understanding, but gives scant weight to the anxieties which the United States, in particular, may show as the guerrillas with their AK-47s begin to fan out over the South African veld. In geo-political and economic terms, the last white redoubt in Africa is the one which matters by far the most.

The dilemma for the Christian, heart-searching Kaunda is likely to be, one day soon, how deeply into one ideological camp he can let himself be drawn by his endorsement of violence for a good cause.