A decade of contacts between the United States and China has demonstrated the vast strength and continuing weaknesses of the complicated web of relationships between two of the world's three most powerful countries.

Ten years ago this week, Richard Nixon concluded his historic mission to China by signing the Shanghai Communique, which laid the basis for normalizing Chinese-American relations after 22 years of hostility. Capturing the spirit of the occasion, Nixon declared that his visit "was a week that changed the world."

There were no anniversary celebrations in either capital yesterday, however. Despite the wide range of new ties between the two countries, leaders on both sides of the Pacific speak pessimistically about the chances of salvaging the relationship from the issue that has proven troublesome for three decades--the defense of Taiwan.

But while the party spirit has soured, Chinese and American officials agree that their current differences over Taiwan should not overshadow the impressive gains in relations during the past 10 years.

The process begun in Shanghai, which flowered into full diplomatic relations in January 1979, drastically altered international alignments with Peking joining Washington and its allies in a new strategic partnership against the Soviet Union.

Normalization also contributed to important domestic changes. In China, it strengthened the hand of pragmatic leaders seeking to modernize, not radicalize their society. In America, serious social tensions aroused by the Vietnam War disappeared once the White House received assurances from China that a pullout of U.S. forces need not end American influence in Asia.

The Shanghai Communique formalized Chinese and U.S. views that their common interest in combating Soviet aggression outweighed any bilateral difference. The Taiwan issue was skirted in 1972 and 1979 with careful statements designed to free both sides to collaborate against Moscow.

The fragile understanding now shows signs of coming undone just as the strategic partnership has begun to mature. With the Soviet Union hovering over Poland and beefing up its forces in Afghanistan, the U.S. side is seeking to enlist Peking in a common response while keeping open its offer of last June to consider Chinese requests for arms.

Peking not only turns a cold shoulder. But it also threatens to reverse the progress of the past decade unless Washington forswears weapons sales to Taiwan, which Nixon acknowledged as far back as 1972 is a part of China.

Officials on both sides now prefer to look back at the decade as a period that enhanced each side's diplomatic flexibility toward a common foe while starting the important process of institutionalizing their relationship by creating new domestic constituencies with vested interests in close ties.

"This is the only place where detente really worked," said a senior U.S. official. "When it comes down to it, we don't have any contradictions except Taiwan. We set the goal of drawing China into a constructive relationship. Fundamentally, it's quite sound."

"In the past 10 years, our relationship has improved the national security of both sides," said a Chinese diplomat. "Taiwan is really the only outstanding question. Otherwise, the relationship is sound."

Snapshots of the decade recall certain dramatic moments that propelled the friendship through public relations. Nixon clinking glasses with Chou En-lai at the Great Hall of the People in 1972. Deng Xiaoping popping out of a stagecoach and waving his cowboy hat at a rodeo crowd in Houston in 1979. Zbigniew Brzezinski peering north over the Great Wall and taunting "the polar bear" in 1978.

The real breakthroughs, however, resulted from the private, painstaking discussions where the framework constructed by Nixon was filled in with dozens of treaties.

Today U.S. wheat farmers sell more grain to China than any other country. Chinese textile factories have turned the American market into their best customer. Overall trade reached $5.5 billion in 1981 after doubling yearly after 1979.

Peking now relies on American expertise to lead the exploration of Chinese offshore oil. About 8,000 Chinese students and scholars are learning American managerial techniques, science and technology at U.S. schools.

Although the potential economic benefits may have been on the minds of the architects of normalization, it clearly was the common security obsession with Moscow that sent Henry Kissinger to Peking for secret meetings in 1971.

The Shanghai Communique contained the first joint denunciation of Moscow with a clause declaring that each side is opposed to "hegemony" in the Asia Pacific region, a clear slap at the Soviets.

Sinologists now see that clause as one of the first public signs of Chinese willingness to enter into an anti-Soviet entente with the United States, Japan and Western Europe.

China's foreign policy shifts have made it possible for Washington to maintain its influence in Asia without the heavy burden of a large military presence. Much of the region's tension has been eased by Peking's advocacy of U.S.-Japanese defense ties, its courtship of the noncommunist governments of Southeast Asia and its quiet endorsement of U.S. troops in South Korea.

Peking's campaign to reunite Taiwan by peaceful means has made it possible for Washington to withdraw its defense umbrella from Taipei and for one of the world's hot spots to cool down.

As a strategic counterweight to the Soviets, China simplifies defense obligations of America and its European allies by tying down 46 Russian divisions--between 750,000 and 1 million men. Its assistance to Afghan guerrillas fighting Soviet soldiers and to resistance forces trying to drive Soviet-backed Vietnamese troops out of Cambodia is consistent with U.S. goals of frustrating Soviet ambitions in the region.

For China, the strategic benefits of normalization are no less significant. The most important cited by Chinese officials was removing the United States from Peking's civil war with nationalist Chinese who fled to Taiwan after the communist takeover in 1949.

"That ended the threat from our east," said a senior Chinese official. "It allowed us to concentrate on the threat from the north Soviet and the one from the south Vietnamese ."

The visit of an old cold warrior like Nixon conferred on China a respectability that facilitated its entry into international organizations and cleared the way for commercial and diplomatic contacts with American allies that had been reluctant to be dragged into a Sino-American feud.

Chinese and U.S. diplomats agree that equal importance should be attached to the forging of institutional groundings essential for an enduring, constructive relationship.

When Nixon came here 10 years ago, only a handful of senior leaders on both sides were involved in the birthing of the new friendship. After 30 years of Sino-American enmity, the U.S. government had few officials working on China except in enforcing the trade embargo and immigration restrictions.

In China, not only were few people studying America, but those with American ties were persecuted during the Cultural Revolution.

Sinologists like Michel Oksenberg, who served on president Jimmy Carter's National Security Council staff, believe that Sino-American ties will remain inherently volatile until they are deeply rooted in each side's bureaucracy and society where they would be difficult to dislodge for frivolous reasons.

The Shanghai Communique began building a lasting structure for the relationship by setting guidelines for development of trade, scholarly exchanges and cultural contacts that gradually broke down suspicions and demonstrated new possibilities.

The process was accelerated under Carter, with agreements covering science and technology, tourism, maritime problems, trade, culture and textile import quotas.

Thousands of U.S. and Chinese officials have traveled across the ocean for meetings that initiated cooperation vital to their jobs. Thousands of U.S. businessmen have talked trade with their Chinese counterparts. Thousands of Chinese students, and a much smaller number of Americans, have studied in the other's country.

"The last decade has seen a basic stability built into the relationship with the emergence of constituencies on both sides that have vested interests in good relations," said a Western diplomat. "Even if the whole relationship unravels over Taiwan, there's a good foundation to build on in the future."

The number of U.S. specialists in China's Foreign Ministry has tripled since 1972, according to Chinese sources, and hundreds of elderly officials who were educated in America during the 1930s and 1940s have been plucked out of unrelated jobs to deal with U.S. affairs. A think tank was set up here last year to investigate American governmental, social and economic problems.

For the increasing number of Chinese involved in bilateral relations and for the Chinese progressives now running the nation, the American connection plays an important role in domestic affairs.

Leaders have used the potential for U.S. technological transfers to fortify their cases for economic modernization with old-fashioned capitalist incentives.

When party Vice Chairman Deng Xiaoping, who leads the modernization faction, visited the United States in 1979, his televised tour of modern factories and the space center is said to have reenforced his argument against economists who advocate nonmaterial incentives to spur the economy.

"It was a real eye opener," said a Chinese official. "No one even really knew what modernization was about."