One of the principal causes of this week's dramatic breach in Soviet-American relations is the Kremlin's growing belief that the United States cannot be trusted to follow through on commitments made by its presidents, even those in signed agreements.

Senior Communist Party officials in private conversations with Americans expressed exasperation over what is regarded here as the Carter administration's ill-considered decision to, in effect, abandon the Vladivostok accord on strategic arms in favor of a wholly new concept of steep reductions.

"Truly," declared Soviet Foreign Minister Andrei Gromyko at his unusual and extremely blunt press conference Thursday, "what will happen if the arrival of a new leadership . . . scraps all the constructive things that were achieved in relations with other countries? What stability can be talked about in relations between the U.S. the U.S.S.R. in this case?"

If this were the first instance of a radical American shift on a major piece of bilateral business, the Soviets say, they would probably not have reacted quite so sharply. But they contend that there is a lengthening list of precedents for turnabouts, abrogations and significant modifications by the United States after - as far as the Russians were concerned - a deal had been struck.

"We've come to the opinion that you can't really count on American governments to carry out promises made on the highest levels of leadership," said a member of the policy-making party Central Committee. "Frankly, you have a serious problem of credibility with us."

The Soviets cite as perhaps the greatest disappointment before now the fate of the 1972 U.S. Soviet trade agreement signed by Communist Party leader Leonid Brezhnev and then-President Nixon during their first summit meeting. Provisions of the pact were never implemented because Congress, after a long delay, linked the extension of trade benefits to freer emigration of Soviet Jews and set limits on U.S. government-backed credits.

In renouncing the agreement early in 1975 the Kremlin said that the congrressional action violated both the letter and the spirit of a document to which both sides and solemly attested.

"Our people recognize that there are differences in our political systems and our procedures," said the Central Committee official." Our political decisions take a long time to reach, perhaps too long, but once they are adopted they are implemented and not immediately subject to changes."

The problem does, in fact, stem from the fundamentally divergent nature of decision-making in the U.S. and Soviet system. Whereas the Politburo runs the state here and its collective power is unassailable, the American President has to submit to a multitude of very strong legislative, judicial and even strong legislative, judicial and even bureaucratic influences, particularly on so sensitive an issue as U.S.-Soviet relations.

THe result from the Kremlin point of view is an often infuriating gap between official American word and deed.

The Vladivostok strategic arms accord of November 1974 was actually a statement of intent negotiated and approved by Brezhnev and then-President Ford, a framework for a long-term nuclear arms control accord. It was not a pact or a detailed agreement, although the Russians clearly regarded it as a commitment to certain broad terms.

"The United States and the Soviet Union," Gromyko said on Thursday, exchanged relevant official documents which sealed the Vladivostok accords. Everything, it seemed, was clear and it remained only to carry the matter forward to the signing of an agreement. At first things were moving, but all of a sudden a wall had risen and everything was frozen. Apparently somebody, some influential forces in the United States, found all this not to their liking . . .

"Great difficulties arose and these difficulties have of late increased even further."

The deadlock to which Gromyko referred concerned whether the U.S. cruise missiel and the Soviet Backfire bomber were to be covered. The Russians insisted that the cruise was and Backfire was not. The Americans held out for controls on both, and former Secretary of State Henry A. Kissinger essentially reached a compromise with Brezhnev on the issue in January 1976.

Progress then halted once again - this time, Ford has since acknowledged, because of strong resistance from the Pentagon and the President's own unwillingness to tackle the delicate matter in an election year.

In addition to its proposal for setting aside the Vladivostok framework altogether, the Carter administration suggested to the Soviets this week a fallback plan for ratifying Vladivostok while leaving aside Backfire and cruise for later negotiations. The Soviets say that this idea involves an unconscionable abrogation of earlier understandings. Hence the Kremlin Judgin from official American comments here over the last week, Carter and his advisers plainly made a significant miscalculation in their initial dealings with the Soviets. They thought that Brezhnev's public assertions that Valdivostok remains the only acceptable basis for a strategic arms accord was merely a negotiating ploy. The President also clearly underestimated Soviet indignation over his stand in support of dissidents here.

"It is amazing to us," said another high-ranking Soviet, "that Mr. Cater would send (Secretary of State Cyrus) Vance to Moscow with the new and tough demands from us that ignore the past and at the same time make us the brunt of his Sunday-preacher moralizing on human rights. How can he expect compromise under those conditions? It is a very difficult situation."