JONAS SAVIMBI A Key to Africa By Fred Bridgland Paragon House. 512 pp. $21.95

THE PART OF Africa to which Jonas Savimbi is "key" is the southwestern territory of Angola, for five centuries a Portuguese colony until it became independent in November 1975. It is an enormous country, twice the size of Texas, bounded on the west by the Atlantic, on the north by Zaire (Congo), on the east by Zambia and on the south by Botswana and the South African-controlled territory of Namibia. Its population is tiny -- only half that of Texas -- but it is rich in minerals, in the year of independence producing diamonds and iron ore equal to a third of South Africa's output.

Those totals have since much diminished, for Portugal's departure from Angola turned the independence campaign that had afflicted the territory for 15 years into a violent civil war. Like most wars in Africa, the Angolan is deeply tribal, but it has also taken on ideological ballast. The victors of the independence struggle, the Popular Movement for the Liberation of Angola (MPLA), drew heavily for its membership on the "assimilated" Africans of the north. They have adopted Marxism and are supported by the Soviet Union, which finances a surrogate army of Cubans under their colors. Their opponents, the National Union for the Total Liberation of Angola (UNITA), draw their strength from the un-Europeanized tribes of the south and, under the leadership of Savimbi, are waging a successful war against the MPLA with South African and covert American support.

Savimbi's motivation is ambiguous. John Stockwell, by Bridgland's account once responsible for the CIA's Angola Task Force, is quoted as alleging that Savimbi "has no ideology. He believes in nothing beyond his own selfish ambitions, and fighting has become his way of life." Savimbi, on the other hand, claims that he represents an African alternative to Marxist-Leninist liberation theory. He argues that Africans are united by a belief in a supreme Being, whatever name that Being is called by, and that any atheistic creed is alien to the essential African spirit. He puts his own faith in the simplicity and common sense of the African "peasant," whom he believes he is destined to lead into a distinctively African future.

Savimbi is no peasant himself. By background he belongs to the "assimilated" class that provides the leadership for his MPLA opponents, and he is highly educated, the graduate of a Swiss university and a fluent exponent of Western political ideas. Nevertheless, he hated the Portuguese as fiercely as any Marxist freedom fighter and, but for the kindnesses of a Portuguese teacher and a Brazilian missionary, would have equally hated all whites.

Because he decided in youth that all whites are not bad, he has been able to accept help from the United States and even from South Africa -- without which, by any objective reckoning, his movement would not have survived. As it is, the area that he controls is the poorest and least populated in the country and his prospects of doing anything more than denying possession of it to the MPLA must now be judged highly doubtful.

Why, then, does Bridgland reckon him a "key to Africa?" The answer, one suspects, has to do with a case of personal over-exposure. The author knows Savimbi very well, has followed in his footsteps over countless miles of Angolan bush and has fallen victim to his powerful charisma -- in the same way that Frederick Forsyth fell victim to the equally powerful charisma of Gen. Chukwuemeka Odumegwu Ojukwu in Biafra during its secession from Nigeria in 1967.

Bridgland's book has defects separate from his addiction to its central subject. First among them is a failure to explain to the reader where Angola is, the nature of the war being waged there and why an intelligent Western reader should take an interest in its outcome. Second is the absence of any apparent concern to construct a comprehensible narrative. "It scarcely seems possible," the author writes in his first sentence, "that this book is at last finished" -- words that any reader who persists to the last will fervently echo. Bridgland, who no doubt is an excellent reporter, is an abysmal biographer, prolix, rambling, repetitive, inconsequential and apparently incapable of putting his hero into perspective.

This is a pity, because Savimbi is an interesting figure -- but only insofar as he is represented within the context of the "South African connection." It is South Africa that is the "key" to the part of the continent where Bridgland has spent so much of his reporting life. Savimbi, for all his intelligence, would have flickered out like a glow worm in the Angolan dusk but for South Africa's support. That he survives is a tribute to the extraordinary power that two million Afrikaners continue to exert in the black continent and the skill with which they project it far beyond their border. That should have been Bridgland's story. Perhaps with time and another publisher's indulgence he will learn how to tell it.

John Keegan, author of "The Face of Battle" and "Six Armies in Normandy," is defense correspondent of the Daily Telegraph of London.