The Tibetans' long struggle to persevere in the face of oppression; In Exile From the Land of Snows, by John Avedon. New York: Knopf. 386 pp. $18. 95.

The fate of the Tibetan people is among the most compelling questions raised by the 35 years of Communist Party control in China. Tibet is a historically independent nation, and its absolute fealty to the tenets of Buddhism helped sustain a system of theocratic rule for close to 400 years. Then, early in 1950 , it lost its independence to the advancing troops of the Chinese People's Liberation Army.

China's unprovoked invasion was undertaken ostensibly to free Tibet of what the newly established Chinese Communist government called ''imperialist oppression'' (although there were only three foreigners in all of Tibet at the time). It set in motion a campaign of brutal repression that culminated in the destruction of more than 95 percent of Tibet's ancient temples and monasteries and the imprisonment of an estimated 25 percent of the Tibetan population at the height of the Chinese Cultural Revolution.

John Avedon's ''In Exile From the Land of Snows'' represents the first thorough accounting of the impact of Chinese control in Tibet. Relying largely on the testimony of Tibetan exiles in India and a series of interviews with the spiritual and temporal leader of the world's 6 million Tibetans, the Dalai Lama, this skillfully written and well-documented book recounts the Chinese government's efforts to bring a fiercely independent nation of Buddhist monks, nomadic herdsmen, peddlers, and high-altitude farmers into the mainstream of China's emerging Maoist society.

As Mr. Avedon's book makes clear, Tibet in the winter of 1950 could not have been more ill-prepared or more ill-suited for an onslaught of Chinese revolutionary thought and practice. The vast majority of Tibetans still held fast to customs and beliefs rooted in the 9th century. Ritual divinations still served as the wellspring of government policy; the hereditary nobility and the clergy jointly exercised political authority.

The Chinese initially chose accommodation, permitting the Dalai Lama to retain a measure of his authority. By the latter half of the '50s, however, the need to consolidate the revolution in the strategically vital region compelled the Chinese to accelerate the process of social transformation in Tibet. Anti-Chinese protests intensified in response to rumors that the Chinese were preparing to depose the Dalai Lama. The demonstrations reached a climax in the abortive Tibetan uprising of March 1959, during which time the Dalai Lama and many senior members of the Tibetan Cabinet and clergy took flight and the Chinese imposed martial law, which was to last two decades.

From 1959 onward, the Tibetans, having gained a reputation as the most recalcitrant of China's 55 ethnic minorities, were subjected to the full force of the Chinese Communist Party's coercive powers. Temples were converted to granaries and workshops; sacred shrines and monasteries were dynamited; monks were imprisoned or defrocked; teaching the Tibetan language was outlawed.

At the same time, the Tibetan exile community in India was on the rise. Numbering more than 100,000, it undertook the task of preserving the achievements of two millenniums of Tibetan culture. Institutes to perpetuate the teachings of Tibetan medicine and Tantric Buddhism were established; libraries and Tibetan schools were constructed.

Tenzin Gyatso, the 14th Dalai Lama, was at the forefront of this effort. In Mr. Avedon's book, he emerges as a man of rare abilities. A learned prelate and an astute politician, the Dalai Lama today remains the fulcrum of the Tibetan Buddhist faith and the leader of Tibet's government-in-exile.

''In Exile From the Land of Snows'' expertly details both the torment and the irrepressible resolve of the Tibetan people. Its author, one of the most able exponents of complex Tibetan rituals, mores, and religious doctrines, has precisely enumerated those qualities - among them courage, constancy, forbearance, and piety - that have enabled the Tibetan people to withstand years of chaos and anomie on ''The Roof of the World.''