CHINA'S FATE: A People's Turbulent Struggle with Reform and Repression 1980-1990 by Edward A. Gargan (Doubleday: $22.95; 332 pages.). " Buxing ," writes former New York Times Beijing bureau chief Edward Gargan in this astute book of reportage, is a "generic utterance for all that is not possible in China." "China's Fate" is in many ways a catalogue of what's buxing in that nation today, and culminates, of course, with a vivid, first-hand account of the bloody events of June 4, 1989. A China scholar before turning to journalism, Gargan obviously was pessimistic about the chances of true reform even before the massacre, and in the book he often criticizes the United States for its too-rosy assessment of the current regime. The most interesting sections deal with the country's people rather than its politics, like the factory official embarrassed to talk about the plant once devoted to Mao badges.