Soviet relations with the United States are at a point of "truly crucial decisions" for completing a nuclear arms control pact, with the future of U.S. Soviet detente riding on the outcome, the Soviet Union declared yesterday.

It is up to the Carter administration, the Soviet Union contended, "whether the agreement is to be or not to be."

A major article in the Communist Party newspaper Pravda, clearly signaling what the Kremlin leadership wants to convey, charged the United States with vacillating and hesitating on concluding the drawn-out negotiations.

This is "not merely the question of just another agreement," the 3,400-word Pravda article said. "The question is actually about selecting the road for years to come."

A failure to conclude the accord, it said, "would mean torpedoing the Soviet-American dialogue on vital questions of security, and a considerable deterioration of the overall atmosphere in USSR-USA relations."

The Pravda commentary attracted immediate attention from senior American officials, because it coincides with what is believed to be a major stock-taking by the Kremlin on the Carter administration.

President Carter, in a March 17 speech at Wake Forest University, raised sharp questions about the direction in which Soviet policy is headed. The Pravda article, in effect, represented an extensive response, intended to pin responsibility on the United States for what lies ahead.

The Soviet commentary headlined "Soviet-American Relations: Time of Crucial Decisions," was in the form on an article by Georgi A. Arbatov, director of the Institute of the U.S.A. and Canada, and adviser to the Politburo on American affairs.

The nature and prominent display of the article signified an important Communist Party pronouncement, rather than the views of just one individual or Soviet institute.

American specialists in Moscow and in Washington construed the article as a significant sign that the Soviet Union was signaling that its relations with the United States are at an important juncture, and could lead in either direction. "They don't lightly talk about being at a crossroads," said a senior U.S. specialist on Soviet affairs.

The "central question in USSR-USA relations," the Pravda article said, is the delay in completing the nuclear strategic arms limitation talks (SALT), which now have "reached a kind of a landmark."

In unusually direct terms, the article depicted the Carter administration as torn between two kinds of political forces in the United States: one force "building up tension," the other displaying "strong tendencies toward detente."

Heading toward a completion of the SALT negotiations, the article acknowledged, will lead the Carter administration into "an involved struggle" with Congress to ratify a new nuclear accord.

"It is quite probable," Arbatov wrote," that one of the causes of the hestitations manifested by the U.S. administration is precisely that fact it has not decided yet whether it is prepared at this time for such struggle.

"One may assume that the opponents of the agreement count on this too . . . to enhance the vacillation of the government and thereby drag out indefinitely the talks themselves . . .," the article said.

"In preparing any agreement, there is a time for expressing doubts and for diplomatic maneuvers," Arbatov wrote. "And there is a time when one must finally decide: will there be an agreement or not."

The article acknowledged that the "overall political atmosphere" has been impaired by the clash of American and Soviet interests in the Horn of Africa. There, Ethiopian troops reinforced by Cubans and Soviet military advisers overwhelmed Somalian troops in Ethiopia's Ogaden region.

But Arbatov scorned attempts to "link up" the SALT negotiations with that conflict, in which he repeated the charge that the United States encouraged Somalian "aggression," an assertion the Carter administration has repeatedly denied.

The article said that President Carter, in his Wake Forest speech, was invoking an imaginary "Soviet threat" to justify "strident promises to strengthen the military might of the U.S.A." In a series of questions, Arbatov asked whether this represents a return to "the 'policy of strength'" and unsuccessful attempts "to attain military superiority . . ."

The basic problem for the United States in its attitude toward the SALT negotiations. Arbatov wrote is "the reluctance to reconcile itself to . . . (military) parity . . ."

He said the fate of the agreement depends today "not so much on the skills of the negotiators, as on the substantial political decision of the U.S. government - whether to conclude the agreement at this time at all . . ."

Almost the exactly opposite contention was made earlier this month by presidential security adviser Zbigniew Brzezinski.

He said, on March 1, that "the problems in SALT which have necessitated a slow pace are real. They are not political. They are not articial. They are genuinely complicated and difficult issues. And we have made reasonably good progress on them. But on some of these issues, I think an act of political will will be required to resolve them . . . And that of course is bound to be complicated by the overall international context."

Numerous other administration sources have said in private that in recent months it was the Soviet Union which made the most concessions for progress in the SALT negotiations in Geneva. Some officials argue that the Soviet Union was moving from the most extreme position, while others credit it with greater flexitility.

President Carter recently gave new instruction to U.S. negotiators to accelerate the drive for a compromise, instructions which privately encouraged the most staunch administration advocates of arms control.

There have recently been hints from Soviet officials in the United States that Soviet leader Leonid I. Brezhnew might possibly decide to attende a special United Nations conference on disarmament, which opens in New York on May 23. If he should appear, that could provide opportunity for a Carter-Brezhnev meeting.