A genuine child of the revolution, Hu Yaobang has become one of China's six most powerful men.

Once disgraced but now rehabilitated, Hu, about 64, is being touted as a candidate for the future leadership of China. He owes his new-found favor to one man, Communist Party Vice Chairman Deng Xiaoping.

Hu, who left his Hunan peasant family in his early teens to join the communist forces, has shared the dizzying ups and downs of his wily political patron for 40 years. He and Deng disappeared from sight together in 1966 when Red Guards accused them, among other things, of setting up a private club and spending working hours pursuing a mutual obsession with the game of bridge.

When Deng returned to power in 1973, Hu was with him. When Deng disappeared again in early 1976, Hu also vanished. But now Deng has consolidated his latest political gains in a far-reaching purge of adversaries and a rehabilitation of his own now dead ally and patron, former president Lui Shaoqi.

Deng has chosen this moment to give Hu a place on the Politburo standing committee and the key job of Central Committee general secretary. Deng acquired the identical job 24 years ago.

Because he has operated so closely with Deng since they fought the Japanese together in the Taihang Mountains in the early 1940s, Hu's own individual strenghts and style have been obscured, and his ability to hold power after Deng's death remains in doubt.

But he has unusual credentials for leading China the rest of this century. His years as a top Communist Youth League official give him wide-ranging ties with China's second generation of communist leaders, and he possesses the useful aura of a man who was just barely old enough in 1934 to participate in the Red Army's famous Long March.

Hu had little formal education, having joined the children's corps of Mao Tse-tung's forces in his native Liuyang County when he was perhaps no older than 12. He did much party youth work, attended a special party school after the Long March and after liberation in 1949 served as an administrator in Deng's native Sichuan. He rose to head the Communist Youth League until the Red Guards destroyed it in 1966.

In the last two years Hu has been Deng's broom, sweeping through the party's personnel mess, clearing out Maoist ideologues, searching for ways to inspire China's disheartened youth to pitch in to energetic party work.

He shares his boss's humble looks, including receding hairline and crewcut. His speeches read exactly like Deng's. But the Peking grapevine gives him a useful reputation as a humane fixer. People say Hu toils to work out ordinary workers' housing and other personal problems, the great obsession of Chinese in the early 1980s.