China now and then; China: opening a door to the world; Coming Alive: China After Mao, by Roger Garside. New York: McGraw-Hill. $12.95 .

Journalists and Sinologists have written several fine books about China over the past year or two. This may be one of the finest. Roger Garside was a first secretary with the British Embassy in Peking from the time of Premier Zhou en-lai's passing, in January 1976, until the upsurge of the movement for democracy and human rights in the winter of 1978-79. He had previously served in China during the darker days of 1968-70.

For Garside, who is fluent in Chinese and fascinated with every aspect of life in China, the story of China after Mao is one of a nation coming alive again after a mad, traumatic period which set it back as many as 15 to 20 years in some fields and even more in others. According to Garside, during the Cultural Revolution, which was launched in 1966, China "lost a generation of trained minds and a generation of thought."

In tracing China's recent moves away from totalitarianism and the Soviet economic model toward a rule of law more tolerant of diversity, Garside may prove to be too optimistic. But the strength of his analysis, combined with his excitement at seeing a nation so long repressed regaining consciousness, gives the book its power.

In analyzing Peking's leadership struggles, the author never loses sight of the Chinese people. He shifts gracefully from an analysis of the Chinese economy and a government decision to allow country people to sell handicrafts in the city streets again to a description of a solitary peasant peddler bedecked with an array of wildly spinning toy windmills made of wood and pink plastic:

"There was not a potential customer anywhere in sight, but the peasant hawker was not in the least dismayed. He was enjoying his freedom to sell the work of his hands and to stroll in the city to marvel at the concrete monstrosity of the modern world. he reminded me of the street vendor created by Jacques Tati in his film 'Mon Oncle,' whose mild anarchy and humanity are at odds with the highly regimented and automated world around him."

A chapter on government policy toward literature and the arts allows Garside a chance to tell the story of the woman writer Ding Ling, who in the 1930s and ' 40s looked on the Communist Party as a liberating force against the corruption and repression of Chiang Kai-shek's government. Released from a Nationalist jail, she was considered a party heroine -- but not for long. Her protests against the incompetence, elitism, and male chauvinism of certain senior Communist Party leaders were not appreciated. She also protested against the intellectual straitjacket of the party line. She was purged, disappeared without trace, survived a dozen years of hard labor and five years of prison, and then reemerged at a congress of writers and artists in 1979, gray-haired but undaunted.

Anyone who can now go to Peking and see the women bringing bright color into their dresses knows that interesting things are happening. China is indeed coming alive. Garside goes on to make even the Politburo seem interesting. Today's headlines about leadership changes in Peking take on new meaning.

One of the heroes of the book is Vice-Chairmand Deng Xiaoping, the diminutive pragmatist who likes to play the simple country boy but whose climb back to power after three purges has been anything but simple.

Garside explains why China's most powerful leader must proceed through periods of stop and go. In carrying out reforms and opening the country to foreign influences, Deng has to strike a balance between democracy and discipline. A crisis of faith in Marxism-Leninism and the cult of Mao makes the situation all the more volatile.

But the author thinks the trend toward reforms, the loosening of controls, and the opening of China to the outside world are likely to continue because they have mass support.

"Today's struggle to open China is backed by a mass of ordinary citizens who, starting in 1976, have shown where their allegiance lies," Garside says.

Farther on, he adds: "To close the door that has been opened to the world would be as difficult in today's China as to restore the doctrine of the infallibility of Mao. During the 1960s, the nation had such a profound and prolonged demonstration of the sterility of autarchy that if one leader or group of leaders tried to close the door he or they would find that their opponents cou ld easily mobilize overwhelming forces against them."