America is a land of enthusiasms, and in the balmy days of 1972-73, when detente with the Soviet Union was in full bloom, Americans were enthusiastic.

Two successful summit meetings portended a new era of political and military cooperation, or so it seemed. A file cabinet full of agreements to cooperate in medicine, science, space, environmental protection and more suggested a great new era of common Soviet-American endeavor.

The American business community set a new standard for enthusiasm with its initial response to this detente. American firms sent legions of executives to Moscow, moved by visions of vast new markets and profits.

American farmers reaped the first serious benefits in 1972-73, when masive Soviet purchases of U.S. grainwiped out American reserves and sent world prices soaring. The domestic price of bread soared, too -- one of the periodic reminders that detente could be complicated.

Then, in October 1973, outside events challenged this new detente, and it could not meet the challenge. The Yom Kippur war that month was the first clear signal that old instincts had not been conquered by the new Soviet-American diplomacy.

The Soviets has advance warning that the war was coming, but they did not share it with the United States. In the closing stages of the fighting, Soviet President Leonid I. Brezhmev sent President Nixon an ominous message threatening to intervene with Soviet forces to protect exposed Egyptian troops, which led Nixon to put American forces on worldwide alert.

Secretary of State Henry A. Kissinger and his associates argued that the Yom Kippur war had demonstrated the value of detente. Despite the tense confrontation, they said, serious trouble had been avoided because both sides had an interest in a peaceful settlement. Like other Kissinger arguments for detente, this one may have been accurate in the subtle terms of international power politics, but for many Americans it did not wash.

By the time of the Yom Kippur war, Washington was preoccupied with Watergate. Detente, like virtually everything else, was pushed aside. A final Nixon-Brezhnev summit in July 1974 did not revive it.

But the first meeting between Brezhnev and Gerald R. Ford, at Vladivostok in November 1974, did revive much of the original enthusiasm. The two leaders reached an agreement in principle on a new strategic arms limitation treaty. The Soviets were elated that "detente survived Watergate," as some of their officials said privately at the time, and the Americans saw hope for resuming the process that the American political scandal has interrupted.

Such hopes were misplaced. A succession of events punctured them. In January 1975, the Soviet Union rejected the Soviet-American trade agreement because Congress had passed the Jackson-Vanik amendment, tying tariff preferences to increased Jewish emigration from the Soviet Union, and then had sharply limited the amount of Export-Import Bank credits the Soviets could receive.

As 1975 progressed, Kissinger and Ford found themselves on the defensive regarding detente. The joint Apollo-Soyuz space flight that summer, and the completion of the Helsinki accords on European security, gave American critics of the policy opportunities to claim that the Soviets were getting one-sided advantages.

One event in the summer of 1975 symbolized the detente problem in the United States. Alexander Solzhenitsyn, the Soviet writer and symbol of intellectual dissent, had come to live in America, and it was proposed that President Ford invite him for a talk at the White House. Kissinger vetoed this idea, a decision that enraged many Americans, including many of Ford's supporters. Ford's refusal to see Solzhenitsyn seemed to many critics to symbolize an American willingness to subvert traditional U.S. values for the sake of a special relationship with Moscow.

In the fall of 1975, though, the two superpowers demonstrated that they could still do big business together. The american labor movement had made an issue of grain sales to the Soviets, complaining that they were forcing up food prices here, and the Ford administration responded with a politically disastrous temporary embargo. But within a matter of weeks, Moscow and Washington agreed on a longterm grain agreement allowing for Soviet purchases of 6 million to 8 million metric tons a year, and more if both sides agreed. (This agreement remains in force even after President Carter's recent reductions in grain sales)

Then the crisis in Angola at the end of 1975 delivered a blow to detente from which it never recovered. The massive airlift of Cuban forces by Soviet planes into Angola to help secure the government of Agostinho Neto, a Marxist, was unprecedented and, to Kissinger and many others, ominous.

Congress refused to allow any direct American response in Angola. But the Soviet-American relationship never again revived. During the election year Ford let it slip intentionally, in part to answer conservative Republican charges that he had gone soft on the Soviets.

The Soviets could not disguise their hope that Jimmy Carter would be elected president in 1976. That January, on the eve of Carter's inauguration, Brezhnev made a carefully worded speech in the Soviet city of Tula that sounded like an invitation to the new American government to turn away from recent disputes and get on with the business of detente. Carter Administration

For Soviet officials responsible for studying the United States, it would be hard to imagine a more baffling phenomenon than the Carter administration. Consider the cacophony of conflicting signals the new American government sent to Moscow:

It came into office proclaiming a ne era in world affairs, an era in which the traditional preoccupation with the Washington-Moscow axis would be suppplanted by new, equally important relationships between the U.S. and its allies in the developed world, and between the United States and the Third World. Washington's air was filled with talk of "trilateralism" and the "North-South relationship."

None of this was directly hostile to the Soviets, but it didn't please them either. One purpose of detente, from Moscow's viewpoint, was the enhance Soviet stature in the world; these new Americans seemed to be talking about ignoring the Soviet Union.

An improvised "human rights" campaign began even before the administration formally took office. Secretary of State-designate Cyrus R. Vance had a long meeting in New York with Andrei Amalrik, a dissident Soviet writer exiled in the West whom the Soviets dismissed as a troublemaker. An official in Moscow later noted that Vance saw Amalrik even before he had met with Soviet Ambassador Anatoliy F. Dobrynin.

Then, in the first weeks of his administration, Carter sent a personal letter to Andrei Sakharov, the leading dissident in the Soviet Union. The letter was delivered through the official diplomatic pouch. The new administration said this was a sign of its concern for human rights. The Soviets saw it as direct encouragement for the only opposition movement inside their dictatorial state, a stunning affront.

The new administration sent an erratic stream of signals on SALT from its inception. Carter said repeatedly he wanted arms control, and he spoke in his inaugural address of a world without nuclear weapons. In his first policy action on the arms talks, he abruptly abandoned the Vladivostok accords and told the Soviets he wanted to go in a new direction, toward much deeper cuts in strategic armaments. His idea was applauded in Washington but rejected out of hand by the suspicious Soviets, who felt they had an American commitment to the Vladivostok formula.

In practice if not in rhetoric, the administration quickly decided that this initial approach had been a mistake, and it reverted to Vladivostok as a starting point for SALT II.

There were confusing indications of how the new administration asesessed Soviet policy and how it intended to handle the competitive side of the Soviet-American relationship.

For three years, the Carter administration spoke with two distinct voices on this issue, They were both legittimate American voices and it may be that both reflected elements of Carter's feelings. In Washington, one voice became associated with national security affairs adviser Zbigniew Brzezinski, and the other with Secretary of State Vance. From a Soviet point of view, the two positions were irreconcilable, yet persistent.

Vance became identified as the apostle of reasonableness, of efforts to coax the Soviets' best instinct forward. Despite his early meeting with Amalrik, Vance in office seemed to look for the bright side, and to hold out the sort of hopes for cooperation that the Soviets sought.

In an interview in April 1978 he said that Carter and Brezhnev held "similar dreams and aspirations" for the world.

Brzezinski became known as the hard-liner. He was the architect of Carter's China policy, and he seemed eager to use it as a club to intimidate the Soviets. In the summer of 1978 Brzezinski's eagerness to confront the Soviets caused Carter to rein him in for a time. But later he was unleashed.

The China policy itself has troubled the Soviets. They stalled SALT in Decembert 1978, apparently to protest U.S. recognition of Peking, and watched in alarm as Deng Xiaoping visited the United States early lastt year, then went home to launch war on the Soviet Union's ally, Vietnam.

The U.S. Middle East policy seemingly was designed to exclude the Soviets from the region. The biggest triumph of Carter's term, the Camp David peace accords, struck the Soviets as directly contrary to their interest. They thought they had a deal with the Carter administration to work jointly for Mideast peace. Carter, they felt, broke the bargain.

Indications of the American government's resolve were uncertain. Here the Soviets' views are open to debate. Some analysts, including some in the administration, are convinced that the Soviets wrote Carter off as a weak figure after he did nothing to respond to their airlift of Cubans into Ethiopia in 1978, to keep the shah of Iran on his throne, or to counter the communist coup in Afghanistan or the Soviets' steadily increasing use of Cuba as a military base.

Others think this is a simplistic analysis of complex events. But it is indisputable that, until recent days, the Carter administration gave no hint as to where it would draw a line.

The United States was unexpectedly willing to go into a new generation of U.S. strategic weaponry at the same time SALT II was successfully completed. The Soviets did not like the new MX missile system, and they abhorred the plan to dramatically increase Nato's nuclear forces by installing, on European soil, rockets capable of reaching the Soviet Union. This modernization of European forces evoked a ferocious Soviet propaganda campaign whose purpose was to intimidate European governments, but last month the Europeans approved the plan anyway. Soviet Behavior

Naturally, there is another side to all of this. Soviet behavior during the last three years has caused confusion and alarm in Washington.

Most alarming, at least to harderline figures in the administration, has been the appearance of a concerted Soviet attempt to encircle the Persian Gulf and its crucial oil reserves. One school of thought identified with Brzezinski has perceived a "crescent of crisis" provoked by Soviet meddling in Ethiopia, South Yemen, Iran and Afghanistan, among other nations.

The continued and expanded us of Cuban expeditionary forces, most dramatically in Ethiopia, added to Washington's concerns.

An inexorable Soviet buildup of strategic forces, including deployment decisions on multiwarhead rockets that soon will give the Soviets a theoretical ability to knock out all U.S. land-based missiles has challenged some of the assumptions of the SALT process and has contributed to a climate of suspicion in this country about Soviet intentions.

Soviet refusal to make any substantial concessions to the human rights provisions of the Helsinki accords on European security aggravated anti-Soviet sentiment in the United States. Instead of any palpable loosening of ideological controls, the Soviets conducted a harsh crackdown against dissidents who sought to hold their government to those Helsinki agreements.

(At the same time, the Soviets allowed a huge increase in Jewish migration, now exceeding 50,000 a year, but they got little credit for this in Washington.)

These factors contributed to widespread skepticism in the United States about the strategic arms limitation treaty signed last June in Vienna. For months it has been evident that SALT II might fail to win the necessary two-thirds approval in the Senate, and there seemed little prospect of any congressional action favorable to improved Soviet-American relations in other fields--trade, for example.

Despite all their troubles, though, both the Brezhnev regime in Moscow and the Carter administration in Washington stuck by SALT II until last month. Then the Soviets decided it was no longer worth the candle.