From age 15 to 27, that time when young men learn the most about the world and themselves, the ruler of this most fervent anti-Communist society lived in the Soviet Union, of all places.

That contradiction is just one of several that add to the mystery, and in an odd way explain the success, of Chiang Ching-kuo, the short, shy, bespectacled son of the late General-issimo Chiang Kai-shek who is now this island's premier and undisputed leader.

Chiang has mordernized the economy and developed foreign trade at a rapid clip. Foreign investment, primarily from overseas Chinese, the United States and Japan, has played a major role in introducing mordern technology to the island. In the last two decades, Taiwan has achieved a growth rate of better than 8 per cent a year in its gross national product.

Yet Chiang remains reluctant to publicly shun his father's old advisers and their old ideas about retaking the Chinese mainland.

He has brought scores of energetaic Taiwanese into a government still dominateed by mainlanders who came here in 1949, but at the same time he views sincere , nonviolent advocates of Taiwan independence as nothing more than Communists in sheep's clothing.

In the words of one foreigner who has spent many years here, Chiang Ching-Kuo "sowed some pretty wild oats when he was younger, drinking and wenching," and yet now he insists on austerity in the personal habits of both himself and his subordinates.

To several Chinese and foreign residents who have watched with fascination as this once-feared internal security-chief has turned into agenuinely popular leader, the many sides of Chiang Ching-Kuo are not so surprising given the strange story of his life. All the different forces that have buffetted China in the 20th century have shaken his own life - the stiff Confucianist emphasis on the ritual of his father, the pragmatism and paranoia of the mentors of his youth in Moscow, the efficiency and money-mindedness of the American advisers who came to help Taiwan in its darkest days of the 1950s.

The one great concern of both his admirers and critics here is that there is really no one at the moment who can succeed him. His gasp of Soviet-American personal politics, his appreciation of Chinese legend and social mores and the Kennedy-like aura he inherited from his father cannot be duplicated. At the moment although a diabetic, he seems unusally healthy for a man of 67, and has led something of a charmed life up to now, emerging unscathed from am assassination attempt in New York in 1970.

He was born in 1910 in the mainland province of Cheliang while his father was in japan helping Sua Yaisen organize the Republican Chinese revolution that would overthrow the last imperial dynasty the following year. His parent's marriage had been arranged and later ended unhappily when his father divorced his mother to make a politically profitable marriage with the eligible daughter of the powerful Soong family, now the world-reowned Madame Chaing Kai-shek. The younger Chinang was 17 and at school in Moscow when his father remarried, and the public statement he issued then denouncing his father revealed perhaps as much of the pain of his youth as it did the designs of the Soviets who served as both his teachers and wardens.

He had gone to school in Shanghai for a while and became fired by the revolutionary fevor that was sweeping Chinese youth. It was 1925 when his father and other Nationlist Chinese leaders were heroes to leftist Chinese and were entertaining Soviet adviers when Chiang Ching-kuo asked to join several friends going to study in Moscow. His father did not refuse.

Bu 1927 his father had broken with the Chinese Communists. Chiang Ching-kuo, by choice or not, remained in the Soviet Union. He has never given a full public account of this period, but by most accounts he was sent to Sineria where he fought cold, sickness and disgrace. He also found a Soviet woman who cared for him and he married her.

In 1937, after Chiang Kai-shek reached a reconcilation with Moscow, his son returned to China impressed by the Communist skill at forging links with common people and chilled by their sinlge-mindness. He learned just how effective these talents were as Mao Tse-tung pushed father's armies off the mainland in 1940.

On Taiwan, young Chiang began to work his way around the governement hierarchy specializing in organizing youth and serving in many military and internal security posts.

"For many years he wore a uniform," said one longtime resident, "but in the 1960s when it was evident he was being cultivated to take over some day, he shed the uniform and his title of general slipped out of use."

Chiang had assumed day-to-day control of the government long before his father's death in April 1975. he became, as he is today, a year-round political campaigner, turning up at a construction sites, to shake hands with the workers, dancing with mountain aborigine tribes, appearing constantly whose people happily discovered they coulf all afford television sets.

He now has no obvius successors politics, and would little interest in politics, and would be ruled out anyway in this race-conscious society because they were Eurasian. His half-brother, Chiang Wei-kuo, apparently a son of Chiang Kai-skek and a Japanese woman, has leading post in the army but is not highly regarded.

The future seems to belong to the young Taiwanese Chiang has brought to the vice minister level in the government. Many of them, their friends say, want real independence for Taiwan, and an end to claims that the island is part of China. Such a move could bring Peking to take steps against the island that it would prefer to put off for a few decades. Chian Ching-Kuo, content with the status quo, many convince his young Taiwanese friends of that.