Thirty years ago the communist bloc shattered with the bitter rift between China and the Soviet Union. Today, the world's two largest communist states are picking up the pieces of their long-lost solidarity.

Soviet Foreign Minister Eduard Shevardnadze arrives Thursday to advance the accelerating process of political normalization between the two countries.His visit is expected to lay the groundwork for Soviet President Mikhail Gorbachev's visit during the spring for the first Sino-Soviet summit since Nikita Khrushchev and Mao Tse-tung met for bitterly divisive talks in 1959.

Gorbachev's talks with senior leader Deng Xiaoping and other officials will formally end a freeze on party and government relations that began when the two nations split over ideological and strategic differences in 1960.

Economic and cultural relations have seen steady improvement since the two sides first embarked on political normalization talks in 1982. Trade last year was an estimated $2.8 billion, up from $300 million in 1982.

The two countries will exchange nearly 1,000 scholars this year, compared to 10 in 1983. Sister programs are being formed, joint ventures established and tours conducted across borders once demarcated by barbed wire and bayonets.

China's hard-line stance toward the Soviet Union has softened in the past year as it joins the world trend toward detente and perceives major progress in what it labels the "three obstacles" to normal ties with Moscow.

The most important obstacle, Soviet support for Vietnam's invasion of Cambodia, remains the toughest to overcome. But in August the two sides for the first time met face-to-face on the issue and agreed it was time for Vietnam to get out. China, backer of the anti-Vietnam resistance in Cambodia, has welcomed Hanoi's plans to withdraw its troops by September.

Gorbachev, who has actively pursued an end to Sino-Soviet ill-will, has taken steps to remove the other two obstacles by pledging to end the Soviet occupation of Afghanistan and to reduce by 200,000 men the Soviet troops in Asia - mainly on the tense Sino-Soviet border.

Despite the heady progress, the real interests of China as it strives to bring better lives to its 1 billion people remain in furthering its economic, technological and even cultural ties with the West.

Chinese leaders insist they will never return to the Sino-Soviet relations of the 1950s, when Beijing depended on Moscow's economic largesse and obediently adhered to its strategic interests.

In the early 1950s, shortly after the communist victory over the Nationalists in 1949, the Soviet Union provided China with loans and technical assistance for heavy industry and several thousand military advisers.

But relations rapidly deteriorated, in part because of personal antipathy between Mao and Khrushchev, Stalin's successor.

The turning point was Khrushchev's 1956 denunciation of Stalin.

Mao thought Khrushchev was trying to usurp control of the communist world and said his efforts to ease tensions with the United States were undermining the unity of the communist bloc.

Khrushchev believed Mao's communes and radical socialism were nonsense.

In 1959 Khrushchev rescinded on an offer to supply Beijing with a "sample" atomic bomb, and in the summer of 1960 the Kremlin stopped all aid to China, pulling out more than 1,000 technicians and effectively terminating more than 200 Soviet-backed industrial projects.

The two countries veered close to war in 1969, when fighting broke out along their disputed 5,000-mile border. China claimed huge tracts of land it said Tsarist Russia had seized in "unequal treaties" of the 19th century.

Chinese leaders, partly to unify a nation then in the throes of the leftist Cultural Revolution, launched a campaign to store grain, dig air raid tunnels and move factories into the hinterlands in preparation for a Soviet invasion.

The invasion never came, but throughout the 1970s both sides maintained more than 1 million troops along the boundary. China's assertion that the Soviet "hegemonists" represented the biggest threat to peace was a key factor in the resumption of relations in the 1970s with the United States.

Relations with Moscow only began to improve after Mao's death in 1976 and the emergence of the pragmatic Deng Xiaoping, who says there is no imminent threat of war.