Close observers of American foreign policy here show increasing concern that the Carter administration has decided to shelve U.S.-Soviet detente in favor of building closer ties to Moscow's ideological enemy and unfriendly neighbor to the east - China.

While the Carter administration's maneuvers have been confusing to Moscow, there is a growing belief among these Soviet observers that the United States is intent on arbitrarily changing the rules of detente that have governed U.S.-Soviet relations for much of the 1970s.

These Soviets no longer think Washington is willing to honor the pledges of more trade and technological exchange and a generally broadened bilateral relationship that Henry Kissinger held out to induce the Kremlin into closer ties.

Instead, they see a growing web linking Washington and Peking, a development in which the Americans are described as "playing the Chinese card" in an effort to weaken Moscow.

Right now, top-level Soviet analysts of U.S. policy are deeply perplexed as they search for a formula for dealing with what they regard as a puzzling and unpredictable administration in Washington.

In their public role, these experts use propaganda and self-serving rhetoric to conceal their fundamental concerts, but the views they have expressed recently in private conversations reflect the thinking among the Kremlin's ruling elite.

The Soviets have traditionally viewed the United States with a mixture of admiration, contempt and suspicion.

America's technology, industrial efficiency and economic dynamism have always been admired here, if not always opens. The prospect of sharing American know-how was the lure that induced the Soviets to pursue detente.

Apart from Soviet technological backwardness, there are compelling domestic reasons for the Krembin leaders to modernize their economy and acquire new technology.

This is an aging society - 46 million persons, or nearly 20 percent of the population, are being supported by state pensions - and nearly that many are close to what is regarded as the poverty level. According to official figures, 12.5 million children are receiving state subsidies designed for families whose incomes fall below the poverty level of 50 rubles per person monthly.

Counterbalancing the admiration and the need for American technology are Soviet suspicion of U.S. motives and contempt for a political process that the Kremlin views as confusing and so riven with conflicting interests that it prevents the development of a clear sense of national purpose. The U.S. political system is regarded as a fundamental fault that has made the United States a waning power.

These conflicting perceptions have become more pronounced since Jimmy Carter became president, and Soviet unease with his administration has been increased by their belief that Carter's national security adviser, Zbigniew Brzezinski, is the architect of Carter's foreign policy. Brzezinski is of Polish extraction, and the Soviets think he has an inherent anti-Russian bias.

From Moscow's vantage point, Carter inherited an undesirable situation following Vietnam and Watergate. Moreover, the Soviets see him as the first American president to confront the global redistribution of power that has been under way for more than a decade, but with which American policymakers have yet to come to terms.

Based on this apparent perception of a relative decline of American power, the Soviets embarked on the African ventures in which they using Cuban proxies.

Soviet informants, displaying genuine puzzlement over the outcry in Washington caused by their African policy, point out that when Nixon and Brezhnev agreed on parity in 1972 they acknowledged the notion of "full opportunity" for the two super powers to pursue possibly conflicting policies in the areas in which their vital interests do not collide.

Carter and Brzezinski, these Soviets argue, have sought to deliberately damage relations by denouncing Soviet involvement in Africa while at the same time meddling in internal Soviet affairs. How else, they ask, can one explain Carter's interest in human rights in the Soviet Union as contrasted to his disinterest in human rights in, say, Saudia Arabia or Iran?

Moscow, according to this argument, has tolerated a good deal of presidential meddling to give Carter the opportunity to get acquainted with the Soviet-American relationship.

But the Soviets eventually came to the conclusion that the combination of human rights activism and foot-dragging on trade and transfer of technology was an attempt to change the nature of detente.

Carter's harsh public language and his initiatives have neither restrained the Soviets in Africa nor prevented political trials of dissidents.

Carter's apparent unwillingness to go beyond tough talk would have sharpened the image if indecision and unpredictability in Washington had it not been for the emergence of an active and aggressive Chinese foreign policy directed against the Soviet Union.

Soviet officials say that China is only potentially a great power. Some of them argue, however, that because of the degree of Peking's hostility toward Moscow, the Soviet Union cannot afford to see China modernized and perhaps even armed by the United States or its Western allies.

This is why the Soviets are deeply concerned and why Washington's ties to Peking have become a central issue in Soviet-American relations.

Both private and public pronouncements here have even gone so far as to suggest the possibility of a preemptive strike against China. Even Pravda, the authoritiative daily, last week pointedly warned Peking about the extent of destruction and loss of of life such a punitive strike would entail.

The Chinese emergence into the world thus has produced a curious spinoff in U.S.-Soviet relations.

Moscow's fear of the China of the future provides both considerable opportunities and grave risks for U.S. displomacy.

Kremlin leaders have accepted the fact that Sino-American relations will be normal eventually, but if normalization goes beyond political cooperation into the area of transfer of American technology or arms to China, the Soviets would see a grave threat to their long-term interests.

This could lead to resumption of the Cold War and raise the possibility of war in Asia as the Kremlin moved to cripple China before its power was enhanced by Western technology.

The thrust of the current bitter campaign against China is to tell the Soviet public that the Sino-Soviets breech is irreparable and that Soviets must once again guard against a threat from the east.

In private conversations, Soviet officials are trying to emphasize the risks involved in U.S. use of the "Chinese card."

A shift away from detente, they concede, would involved belt-tightening. But, they say, the Soviet Union is able and willing to mobilize its resources if it must.

If a real Sino-American alliance developed that included transfer of technology and military cooperation, according to this line of thinking, the Soviets would not be willing to wait for China to acquire retaliatory power and cancel out the current Soviet advantage.

The Soviets are quick to point out, perhaps in a self-serving manner, that the interests of Peking and Washington are not identical and that the Chinese are only temporarily using the United States to put pressure on the Soviet Union.