A Terrorist and a Scholar : THE CLAWS OF THE DRAGON: Kang Sheng--the Evil Genius Behind Mao--and His Legacy of Terror in People’s China, <i> By John Byron and Robert Pack (Simon & Schuster: $27.50; 504 pp.)</i>

When the biggest political trial in Chinese history was held in 1981, the Gang of Four, led by Jiang Qing, widow of Chairman Mao Zedong, was physically in the dock. But the presence of the ghosts of three other men was palpable.

These were, first and foremost, Mao himself, who had died in 1976 but who was still officially revered as the founder of the People’s Republic of China; his “closest comrade-in-arms” and would-be assassin Lin Biao, who died in a plane crash while attempting to flee to the Soviet Union, and a third man, Kang Sheng.

After the trial opened--foreign journalists were barred from the courtroom--the disclosures that came out via official channels, primarily television footage of the courtroom drama, were so staggering they numbed the mind.

Kang Sheng, it became clear, had played a pivotal role in the persecution of hundreds of thousands of individuals, including the highest-ranking officials in the government and party; he tortured their friends and colleagues until they could be labeled “enemy agents” or “counterrevolutionary revisionists.”

Huge numbers of deaths resulted from Kang’s ruthless activities over half a century. The deaths between 1966 and 1970 for which documentary references can be found exceed 30,000.

The man who perpetrated such heinous crimes did not look the part. He was thin, almost frail, and the spectacles he wore because of his extreme myopia gave him the look of a schoolmaster. He was an accomplished calligrapher and painter.

He could be charming while discoursing on ancient ink slabs or Song-dynasty landscapes, but he also was cunning, calculating and cruel, willing to sell out both his mentors and his followers. He preferred to remain in the shadows and to work through others without revealing himself, a style that befitted a man whose life’s work centered on the gathering of intelligence.

During the Cultural Revolution, when all China was in chaos, Kang lived in the lap of luxury, having the use of several houses, in which he kept priceless works of art that had been plundered from the homes of others by Red Guards sent at his instigation.

His main house--a sprawling mansion set amid a lovely garden that featured an artificial hill, crowned by a small pavilion and a succession of courtyards leading to a bamboo forest--was converted into a hotel after his posthumous political disgrace. It opened its doors about the same time as the trial.

Kang enjoyed close ties to both Mao and Jiang Qing. He was, in fact, the matchmaker who brought them together in the 1930s and who, some sources allege, had been her lover before that.

“The Claws of the Dragon” is a fascinating portrait of a man whose importance was not fully appreciated by many in and outside China until after his demise. Indeed, when Kang Sheng died in December, 1975, he was hailed as a great revolutionary hero and buried with full honors in the Babaoshan cemetery.

However, within months, Mao himself was dead and his widow and his closest political associates incarcerated. Kang’s family saw the writing on the wall and quietly had his remains removed and reinterred in more modest quarters.

Apparently for professional reasons, the principal author of this book, identified as “a veteran Western diplomat and longtime analyst of Chinese affairs,” has chosen to cloak his identity behind a pseudonym, John Byron. Byron and his co-author, Robert Pack, have done a magnificent job of exposing Kang Sheng as the evil genius behind numerous atrocities sanctioned by Mao.

In this book, all the fascinating characters of the Cultural Revolution appear, both the victims, such as Liu Shaoqi and Deng Xiaoping, and their persecutors, ranging from propagandists such as Wang Li, Guan Feng and Qi Benyu to Red Guard leaders such as Kuai Tafu and the plump female Marxist lecturer, Nie Yuanzi, who wrote the first wall poster. Wang, Guan and Qi were followers of Kang Sheng who were betrayed by him and hauled off to prison without any warning to rot for 21 years.

Kang was born in 1898 into the family of a well-to-do landlord, who sent him to a school run by a German missionary and who, when Kang reached the age of 17, arranged for him to take a bride. He joined the Communist Party in 1924 and, having deserted his wife and two children, married another Communist named Cao Yi’ou in Shanghai. She was to become his partner in crime in later years. Her sister was to become his mistress.

He operated covertly in the dangerous environment of Shanghai, working closely under Li Lisan, an early party leader, before switching his allegiance to Wang Ming, whom he later also abandoned. Kang soon was involved in intelligence work and, in a devious ploy unbeknown to other party leaders, betrayed five aspiring young left-wing writers and poets to the Kuomintang. In 1931, he became security chief.

He was sent to Moscow in 1933 as Wang Ming’s deputy to the Comintern. There, he studied Soviet security and intelligence techniques. He witnessed Stalin’s great purges and followed his example by purging Chinese “counterrevolutionaries” in the Soviet Union.

After returning to China, he switched sides again, abandoning Wang Ming for Mao, who at the time was infatuated with a two-bit actress named Jiang Qing, to the consternation of other Communist leaders. Kang smoothed the way for Mao to marry the tall, slim and vivacious young woman. For this he gained Mao’s gratitude and was rewarded with command of the secret service. In this role, he whipped up spy phobia by arresting a number of innocent residents as enemy agents.

His cruelty was evident during a land-reform campaign, when he resorted to barbarism. Kang ordered his men to cut a hole in the nose of a landlord (who in fact had been sympathetic to the Communists), put a ring through it and tie a rope to the ring. Then he forced the man’s son to lead his father through the streets.

But it was in the Cultural Revolution that Kang really came into his element. His taste for inflicting pain was so notorious that it earned for him a nickname: the King of Hell.

His biggest achievement during the Cultural Revolution was the toppling of China’s head of state, Liu Shaoqi, who died of pneumonia in prison, alone and unattended.

Not satisfied with Liu’s downfall, Kang declared Liu’s wife an American spy because she had been born in the United States and spoke English. For good measure, he also pronounced her a spy for the Japanese and the Kuomintang.

He denounced Deng Xiaoping, with whom he had worked closely during the ideological battle with the Soviet Union, as “a Khrushchev-type person.”

With Deng’s second comeback after Mao’s death, Kang himself was posthumously disgraced. But although discredited more than 10 years ago, his political legacy is still evident. He was responsible for China’s backing of Pol Pot, the genocidal leader of Cambodia’s Khmer Rouge, who continues to enjoy Beijing’s support.

And Kang Sheng’s accusation, made 30 years ago, that the United States was “dreaming of a so-called ‘peaceful evolution’ in the socialist countries” has evolved into today’s often enunciated charge that Washington is plotting the downfall of communism in China through “peaceful evolution.”

None of Kang’s deeds during the Cultural Revolution, of course, could have been done without Mao’s acquiescence. The authors depict Kang as the evil genius, with Mao more passive than active. Yet, Mao’s own genius cannot be denied. It may be too early to conclude to what extent each man was manipulating the other.