By Harold T.P. Hayes

Simon and Schuster. 351 pp. $21.95

DIAN FOSSEY was a magnificent eccentric, a true and deep fanatic. The author of Gorillas in the Mist, the famous primatologist lived for 18 years among the mountain gorillas of Africa until her murder there in 1985. The U.S. ambassador to Rwanda recalls her as "difficult, crusty, and obsessed." An official of the African Wildlife Foundation, who knew her, remarks: "Perfectly balanced people don't choose to go live on a mountain in Rwanda." Student researchers who attempted to cohabit her lofty mountain "carry vivid pictures in their minds: Dian Fossey brandishing a machete as she speaks of those who would threaten her gorillas; Fossey, eyes flashing, shaking with rage and screaming obscenities . . ." The Africans in the villages below called her "Nyiramachabelli," which she understood to mean "the old lady who lives in the forest without a man." And the one great love of her life, National Geographic photographer and film-maker Robert Campbell, states: "If I had been a single man, I would not have married Dian Fossey."

Harold T.P. Hayes, an editor of Esquire who died last year, was the author of the article in Life magazine that became the basis -- along with Fossey's own book -- for the popular movie, "Gorillas in the Mist." In this book he expands upon his original research. He seems to have interviewed everyone who ever knew the unkempt, unruly, six-foot-tall, husky-voiced, occasionally beautiful white woman who became in time a greater source of trepidation to locals than the 300-pound gorillas she was studying.

Fossey was born in 1938 and grew up in California, a child of divorce and unhappy affluence. A middling student whose grades prevented her entering veterinary school, she became an occupational therapist, trained to teach crafts to crippled children. She saw herself, we are told, as freakishly tall and flat-chested, socially inept and alone, and launched upon a low-paying dead-end career. She took a job with a hospital in Louisville, where she knew no one but felt there would be horses to look at, and she was befriended by one local family with ties to Africa. She borrowed the money to visit Africa herself. Her safari -- especially her glimpses of gorillas and of wildlife photographers living alone in alpine meadows -- enthralled her, and when she returned to Louisville she wrote about her adventure for the local paper.

In 1966, Louis Leakey, the famous archaeologist, lectured at the University of Louisville. Dian approached him with her news clippings and asked to become his "gorilla girl." Leakey was known for his unorthodox selection of researchers. He preferred untrained women, as he appreciated their dedication and lack of preconceptions. His protege, Jane Goodall, living among chimpanzees in Tanzania, was beginning to produce astounding results, and he wanted to place a similar researcher among the rare mountain gorillas. Fossey lobbied desperately, won his acceptance, quit her job and flew to Africa forever.

Thus it was that a gangly, outcast 37-year-old American woman, in poor physical condition, without scientific knowledge, and speaking no language but English, claimed as her turf a few rainforested African mountaintops, the cloud-piercing Virungas. Her research and observations would alter forever the popular myth of the gorilla, replacing the ferocious stereotypes with portraits of loving kinship groups and gentle behavior. She held the world at bay and fought for the preservation of the wildlife sanctuary in which she lived in the years before international conservationists had a handle on the problem. She probably singlehandedly staved off extinction for her beloved gorillas. But the battles she fought against the press of civilization -- against the poachers, the cattle-herders and the farmers of teeming Rwanda -- became increasingly hysterical and bloody. When she was murdered -- probably by the poachers whose snares she had cut, whose dignity she had abused -- no one who knew her was surprised.

HAYES, who loved Africa, lyrically describes the gorillas' terrain: "The Virungas marked the continental divide, a terrestrial line beyond which the lights went out and the mystery began . . ." He recreates the world of the white Africans, a sort of lost generation of British colonialists who spent their childhoods in the African bush and their college years at Oxford and Cambridge, while in the background the rumbling of the wars of independence begin. His book painstakingly traces Fossey's overnight metamorphosis into Leakey's "gorilla girl," a staff researcher for National Geographic, an autodidact courted by scholars from all over the globe. And it delves into the sources of her unhappiness and her decline into what many read as mental illness. The Dark Romance of Dian Fossey is a fascinating celebrity biography, a revelatory companion work to Fossey's own book.

But her book, Gorillas in the Mist, is of a different order altogether. If one has time for only one Fossey book, it ought to be hers. What Hayes's very readable book somehow fails to capture is the fact that this erratic woman was capable of appreciating and of eloquently relaying images of primeval beauty. She was able to interpret the complex meaning of gorilla grunts and gestures. She was capable of passionately loving the wild apes and of inspiring their trust in her. Desmond Morris long ago wrote, "If gorillas gave awards, Dian Fossey would be a Nobel laureate."

Gorillas in the Mist, Fossey's book, reads like a novel by Tolstoy, a complicated account of the evolution and movement of great family clans and heroic individuals. It has its Prince Andrei in the brave young male, Digit. It is as whole and pure as a work of art, and became famous and beloved for the wonder of the world it described rather than for its scientific precision.

In her own book, Fossey appears as the humblest of observers, crouched in the underbrush, witnessing the interactions of titans. A book that places her at center stage -- where she never wanted to be -- is a lesser work. One would not want to have only the film "Amadeus," for example, instead of hearing Mozart's music. Van Gogh's madness is of interest only if one has treasured his paintings. The fact that Dian Fossey was a crank does not enlarge -- nor should it impeach -- her shining, irreplaceable life's work.

Melissa Greene's book about recent Southern history, "Praying for Sheetrock," will be published next year.