TWENTY YEARS AGO this month the Great Cultural Revolution was officially begun in China. Its ostensible purpose was to purify the nation by silencing those who failed to place their toes precisely on the Maoist line, but its effect was to plunge China into a decade and a half of terror that is likely to haunt it for generations, much as the Holocaust haunts Germany and the Jews. One of its victims was a young man named Liang Heng, a native of the South China city of Changsha whose father, an ardent Maoist, was somehow determined to be a dissident, a label that quickly found its way to his son. But Liang proved a resourceful and intelligent fellow, and a lucky one as well; a talent for basketball helped insulate him from the revolution's worst depredations, and then he fell in love with Judith Shapiro, an American who was teaching at Hunan Teachers College.

In 1980 Liang and Shapiro married, and the following year they were permitted to move to the United States; in 1983 they published a fine account of Liang's early life, Son of the Revolution. They live in New York, where Shapiro is a free-lance writer and Liang -- now an American citizen -- edits a quarterly publication called The Chinese Intellectual, which among other things seeks to promote good will and understanding between China and the United States. Perhaps because he occupies this potentially influential position, Chinese officials have kept silent about the critical portrait he painted of his homeland in his autobiography; in 1984 an official at the Chinese embassy in Washington surprised him by saying that since "great changes for the better were under way in China . . . it was high time I go back and have a look for myself."

So in the winter of 1985 Liang and Shapiro went back: for an emotional meeting with his father and mother in Changsha, for an extensive tour of Peking, Shanghai and Canton, for visits to distant rural areas from which they were supposedly forbidden, for conversations with Chinese at almost every level of society. What they found, as described in After the Nightmare, can only be described as extraordinary. There is no way of knowing, as they point out, whether the reforms authorized by Deng Xiao-ping will have a lasting effect or will prove only a brief respite from China's long history of feudalism, but there can be no question that at the moment the reforms have altered daily life in China to a degree that no one could have predicted even as recently as when Liang left China five years ago. His description of them in After the Nightmare is authoritative, vivid and sympathetic, but scarcely panglossian.

The reforms are complex and sweeping, but they can be divided into two broad categories: those that undo the political repressions of the Cultural Revolution, and those that relax the clumsy grasp of the bureaucracy and the Communist Party on the Chinese economy. Of the former Liang encountered many moving examples, the first being that of his ailing father, restored from disgrace to a position of respect at his beloved newspaper and permitted to move, after a bit of lobbying by Liang, into a comfortable apartment. Two old friends, Peng Ming and Tao Sen, had emerged from imprisonment and were making their way into the new entrepreneurial economy; Tao, the erstwhile "radical democrat," to Liang's astonishment was now working on a plan "to build a small tourist hotel with an attached museum" featuring the work of a noted painter.

The freedom to undertake such an enterprise was granted Tao by the economic reforms, which even more than the political ones have opened a new age in China: "In Tao's view, the economic reforms were making changes no political campaign could, moving China gradually toward a more liberal system. With the emphasis on economic life, the authority of the party seemed to be weakening. In order to permit these small, lively companies to exist, the party could not exert absolute control over them. The new economic organizations thus had the potential for balancing the Communists' excessive power." Everywhere he went, Liang encountered individual instances of the "enormous political and social ramifications" of the reforms. One of these was a poor woman, Mrs. Xiao, who did not know precisely what she wanted to do but knew one thing for certain: "What I want to do now is to go into business and make some money!" Liang reflects:

"I realized how radically the economic reforms had changed the situation of people like Mrs. Xiao. The strength of the individual was being unleashed, the power monopoly of the work unit being broken. Mrs. Xiao was now on a more or less equal footing with other individual and nongovernment entrepreneurs, and it no longer mattered much what her political history had been, or what class background her ancestors had been from. The fringe members of society were moving into the mainstream. How very different than when I was growing up! Then, a person without a unit was like a ship without water, but Mrs. Xiao should no longer need to dread those questions about her job. To some people, her lack of affiliation would even seem enviable, for sometimes, if someone considered very useful to a work unit requested leave of absence to do business, the request was denied."

THIS IS NOT to say that in the China of Deng Xiao-ping, Liang found the new Elysium. Talking with one woman Liang realized that "the nightmare was over and the terror was past, but how could Mrs. Yang's scars and those of thousands of Chinese families ever truly heal?" At a rural community he reflected bitterly that "life in this backward, primitive northern countryside seemed heartlessly cheap." Over and again he found that "in a land where personal relations had long overridden law," a person's "connections" still mattered more than anything else; "I'd like to go into washing machines," one man told him, "but in China you can't drink a glass of hot water without connections." The one-child policy of the new regime may be laudable population-control policy, but Liang found its effects on individual families debilitating and even destructive. It disturbed him, too, that Chinese society had lost touch with its contemporary roots:

"It seemed to me that the disillusionment of people with revolutionary symbols like the Red Army could be understood as one aspect of the current crisis in values, of the materialistic trend and the worship of the West. Without an accepted common myth of its origins and destiny, the life of any nation will seem fragmented and purposeless. China's wealth of shared public symbols was once unparalleled. Now, however, many of them had become devoid of meaning, or poisoned with negative associations. The Red Army, the Long March, the Zunyi Conference, the song 'The East Is Red,' the revolutionary color red, and the image of Chairman Mao himself, his once omnipresent statues, busts and portraits: these symbols no longer spoke to most Chinese people any longer. They had lost their power to inspire and to explain the world."

It further concerns Liang that the new government "could ask the Chinese people to put the Cultural Revolution out of their minds and focus on a glorious, sunshine-filled future." Over and again he emphasizes that the lessons of that terrible time must be learned and never forgotten, because "what had been our greatest misfortune was also our greatest hope, for it offered us a chance to understand, as a nation, the great urgency of liberating ourselves from our tragic past." It is toward understanding that history, as much as toward depicting the new China, that After the Nightmare is directed. In incident after incident, case history after case history, Liang demonstrates that the startling improvements he witnessed must always be viewed against the hell out of which they were wrested. Feudal be weakening. In order to permit these small, lively companies to exist, the party could not exert absolute control over them. The new economic organizations thus had the potential for balancing the Communists' excessive power." Everywhere he went, Liang encountered individual instances of the "enormous political and social ramifications" of the reforms. One of these was a poor woman, Mrs. Xiao, who did not know precisely what she wanted to do but knew one thing for certain: "What I want to do now is to go into business and make some money!" Liang reflects:

"I realized how radically the economic reforms had changed the situation of people like Mrs. Xiao. The strength of the individual was being unleashed, the power monopoly of the work unit being broken. Mrs. Xiao was now on a more or less equal footing with other individual and nongovernment entrepreneurs, and it no longer mattered much what her political history had been, or what class background her ancestors had been from. The fringe members of society were moving into the mainstream. How very different than when I was growing up! Then, a person without a unit was like a ship without water, but Mrs. Xiao should no longer need to dread those questions about her job. To some people, her lack of affiliation would even seem enviable, for sometimes, if someone considered very useful to a work unit requested leave of absence to do business, the request was denied."

THIS IS NOT to say that in the China of Deng Xiao-ping, Liang found the new Elysium. Talking with one woman Liang realized that "the nightmare was over and the terror was past, but how could Mrs. Yang's scars and those of thousands of Chinese families ever truly heal?" At a rural community he reflected bitterly that "life in this backward, primitive northern countryside seemed heartlessly cheap." Over and again he found that "in a land where personal relations had long overridden law," a person's "connections" still mattered more than anything else; "I'd like to go into washing machines," one man told him, "but in China you can't drink a glass of hot water without connections." The one-child policy of the new regime may be laudable population-control policy, but Liang found its effects on individual families debilitating and even destructive. It disturbed him, too, that Chinese society had lost touch with its contemporary roots:

"It seemed to me that the disillusionment of people with revolutionary symbols like the Red Army could be understood as one aspect of the current crisis in values, of the materialistic trend and the worship of the West. Without an accepted common myth of its origins and destiny, the life of any nation will seem fragmented and purposeless. China's wealth of shared public symbols was once unparalleled. Now, however, many of them had become devoid of meaning, or poisoned with negative associations. The Red Army, the Long March, the Zunyi Conference, the song 'The East Is Red,' the revolutionary color red, and the image of Chairman Mao himself, his once omnipresent statues, busts and portraits: these symbols no longer spoke to most Chinese people any longer. They had lost their power to inspire and to explain the world."

It further concerns Liang that the new government "could ask the Chinese people to put the Cultural Revolution out of their minds and focus on a glorious, sunshine-filled future." Over and again he emphasizes that the lessons of that terrible time must be learned and never forgotten, because "what had been our greatest misfortune was also our greatest hope, for it offered us a chance to understand, as a nation, the great urgency of liberating ourselves from our tragic past." It is toward understanding that history, as much as toward depicting the new China, that After the Nightmare is directed. In incident after incident, case history after case history, Liang demonstrates that the startling improvements he witnessed must always be viewed against the hell out of which they were wrested. Feudal China is not a creature of the distant past but a fresh memory and a continuing presence, one that at any moment could drag China back into the dark ages. This is Liang's urgent message: if China forgets that past, it is almost certainly fated to relive it.