The Kremlin's massive foray into Afghanistan closes out a decade in which the United States and Soviet Union tried -- and failed -- to fashion a relationship in which a mutual interest in peace would eventually temper inevitable superpower rivalries.

Even the most committed advocates of Soviet-American detente inside and outside the Carter administration now concede that a period of intense military competition is again under way. The arms race is overwhelming those threadbare remaining efforts at arms control that the Afghanistan operation, experts agree, is almost certainly demolishing.

"The probability," said a senior administration official yesterday, "is that U.S.-Soviet relations will be at a very low level for years to come."

The brute force of Moscow's intervention in Afghanistan, symbolizing the collapse of detente, is confirmation to those Americans who believed all along that the Kremlin would never submerge security interests in an ephemeral quest for better relations with the United States. The invasion, said Sen. Henry M. Jackson (D-Wash), a leading congressional critic of detente, "is the most serious development that has occurred since the 1940s."

For those who favored detente, Afghanistan is merely sorry confirmation of the consequences of failing to persuade Moscow that military restraint is in the Soviets' best interest. "We have no credibility with them in our punishing acts," a Senate staffer observed, "and no rewards to give either for good behavior."

From a high point in the early 1970s when the first strategic arms limitation accord was accompained by solemn declarations of peaceful intentions, pledges of vast expansion in trade and cooperation in a host of scientific, technical and cultural fields, relations have tumbled to a point where little of significance remains.

"The Soviets clearly asked themselves what of value they stood to lose with the United States by going into Afghanistan," a State Department analyst observed, "and concluded the answer was: not much."

Moscow evidently weighed the security implications of the turmoil in Afghanistan -- in addition to the upheaval in Iran -- and decided they were of far greater importance than a SALT II treaty that seemed headed for defeat anyway.

According to this assessment of Kremlin reasoning, America's debate over SALT II has been marked by decisions to drastically increase the defense budget over the next five years, expand the NATO nuclear arsenal in Europe and go ahead with the MX missile system. Instead of arms reduction, SALT, which the Soviets have repeatedly declared the cornerstone of detente, has become the occasion for substantial U.S. arms expansion.

Moreover, the Soviets must now recognize that a deep political suspicion here of Kremlin motives on all fronts, plus the certain competition ahead for declining world energy resources, mean that chances for good relations with the U.S. have disappeared.

Among Americans, however, the prevailing position is that the decision to undertake a major upgrading of the country's defenses is merely a response to the Soviet's own long-term military expansion at home and abroad and increasingly assertive Soviet involvement in the Third World.

In the 1975 Angolan civil war, the Soviets were still content to use Cuban troops as proxies. In Ethiopia in 1978, Soviet advisers were sent in to support the Cubans. Now in Afghanistan, for the first time, the Kremlin has sent its own armies into a Third World nation with the apparent resolution necessary to bring that country under Moscow's firm control.

By this argument, the Soviets' persistent lack of restraint over a long period has finally convinced a decisive majority of U.S. public opinion that the only way to deal successfully with the Kremlin is to outgun it.

Largely forgotten in the rush of events is that the 1969 beginnings of detente in SALT I actually came while the U.S. was still deeply embroiled in the Indochina war and only 18 months after the Soviet invasion of Czechoslovakia. And the summit signing of the SALT accord in May 1972 came as the United States was engaged in the most intensive bombing campaign in history to block a Soviet-supported North Vietnamese offensive in South Vietnam.

Despite the inauspicious timing, a political will plainly existed in both capitals to find a way that would sharply limit -- and eventually eliminate -- the likelihood that the superpowers might find themselves in a nuclear conflict.

What went wrong and how blame should be apportioned will be the subject of prolonged analysis by scholars and experts. But an initial conclusion shared by many who have watched Soviet-American relations deteriorate in recent years is that neither side understood the other's politics well enough to make the right compromises.

To take one little-noticed example: Two treaties setting limits on underground nuclear testing were signed by Soviet and American leaders in 1974 and 1976. Neither was ever submitted to the U.S. Senate for ratification because the administrations of President Nixon and Ford were certain once they were signed that they would be defeated.

In Moscow, this inaction, and the absence of a full explanation for it, were perceived as a serious rebuke to the Kremlin.

But in Washington, the Soviets were criticized for insistence on various bargaining positions viewed here as unacceptable. The result: stalemate.

Another explantion for detente's failure is, as a senior administration official put it, that international politics has injected a series of major obstacles that emphasized the competitive rather than cooperative aspects of the superpower relationship. In Africa, Southeast Asia and the Middle East, each country became irresistibly drawn into local conflicts without real regard for the impact on the other's sensibilities.

"Detente," said one long-time supporter of a modus vivendi with the Kremlin, "petered out because the political climate kept getting worse and no one was really willing to take the risks to set things right."

The essential end of the 1970s effort to reach accommodation does not mean that all aspects of Moscow-Washington relations are at an end. The possibility of changes in the leaderships there and here could bring renewed impetus. Past relations have worsened and then improved a number of times.

In the meantime, the United States continues to sell large quantities of grain to the Soviets because such sales are in the interests of American farmers and Soviet consumers.

The Soviets also are continuing to permit substantial emigration of Jews -- almost 50,000 this year -- in response to a strong campaign on their behalf in the West.

But important as these moves may be those involved, they are outside the heart of what detente was meant to achieve -- a gradual, sustained and ultimately irreversible reduction in international tensions. On that score, the record for the decade is poor.