The Carter administration seriously miscalculated the impact and the consequences in the Soviet Union of the U.S. plan for deep cuts in nuclear armed forces, informed American sources privately concede.

In public, administration spokesmen have said the United States was "not surprised" by the swift, total rejection of the dual American arms control proposal. In fact, the negotiators led by Secretary of State Cyrus R. Vance were badly taken by surprise, and the long-range consequences of the failure are totally unknown.

Virtually nothing that happened to the American nuclear strategy in Moscow matched the official "game plan." Before the Vance mission left Washington last Friday, there were deep apprehensions among many U.S. strategists about what would happen in Moscow to a strategy officially decided upon conclusively only two days earlier by the National Security Council, and never fully "staffed out" across the government in the form it emerged.

According to all indications during the Vance mission, President Carter personally set the strategy for a combination of domestic and international objectives.

All available information points to those objectives as an attempt to bargain off hardliners in the Pentagon and in Congress now, by showing he could "hang tough" with the Soviets in order to set the stage for subsequent substantial arms limitations. That would require ultimate compromises and probably going over the heads of the President's internal opponents to reach the American public.

The President may feel justified that despite the failure in Moscow, his personal strategy is still valid informed sources speculate. But numerous American specialists are privately stunned by the uncertainties that now open up. "The President," one highly-informed U.S. source said, "showed he can bargain with the Pentagon and 'Scoop' Jackson. [Sen. Henry M. Jackson (D-Wash.] -- but not with the Russians."

This is where U.S. strategy seriously miscalculated, according to insiders:

The Soviet leadership not only refused even to ask questions about the two-option U.S. offer, after studying it overnight, which was rated as the absolute minimum expectation, but they refused to attempt even to exploit it. They spurned what was thought to be the simplest Soviet counter -- to try "to pick the raisins out of the cake" by dipping into the two options to select out of them a counter-offer that would fully serve Soviet interests.

This showed American negotiators there was a fundamental mis-estimate of the Soviet scene. One planner said ruefully, The Russians had shifted totally out of their normal pattern." The basic U.S. premise was erroneous.

Soviet leader Leonid Brezhnev was found to be in "surprisingly deteriorating" physical condition. This was seen as almost ruling out any prospect that he would attend a summit meeting in Washington to confirm a new strategic arms limitation talks (SALT) accord, even if one is reached. This was the goal set in November 1974, by former President Ford and Brezhnev when they met at Vladivostok, to be fulfilled in 1975, or at the latest, 1976, before the American presidential election.

Brezhnev's condition virtually removes that leverage from the U.S. bargaining hand. If he cannot attend a summit meeting, his personal attitude toward the SALT negotiations may have fundamentally changed, especially if the United States continues to pursue the "hang tough" strategy.

The Soviet indignation over the tough bargaining demands laid down by the United States, in what officials now privately concede should have been regarded as "an opening move," not "a take it or leave it demand," may be genuine, and not tactical.In that event, the Carter administration also may be badly overestimating its ability to make compromises that the President can sell, first domestically, and then to the Soviets.

President Carter ruled against widespread recommendations inside the administration to handle the Vance trip as "an exploratory mission," like his middle east trip in February.Even the Joint Chiefs of Staff are reported to have favored this milder approach, to avoid confronting the Russians with drastic changes in SALT bargaining so early by an untested, still-organizing, Carter administration.

One almost certain Soviet counter to tough U.S. bargaining terms, U.S. specialists cautioned, would be a threat to revoke the concession the Russians made at Vladivostok to drop Moscow's call for liquidation of U.S. air bases in Europe. Vance said yesterday, en route to Paris, that this threat publicly aired Thursday by Soviet Foreign Minister Andrei Gromyko could result in a "total change" in SALT negotiations.

Although U.S. officials privately say the spurned U.S. terms may indeed appear "one-sided" to the Kremlin in their present form, when "bargained-out" they would be seen to be equitable. One expert, nevertheless, whose attitude is privately shared by others, said the Soviet Union would have never agreed to receive the Vance mission if the Kremlin had seen the detailed U.S. proposal in advance.

President Carter, and Vance, both have said they see no real evidence in the talks that U.S. support of dissidents and human right in the Soviet Union was linked to Soviet rejection of the U.S. offer. Many experts agree that if the U.S. SALT offer was attractive enough to the Kremlin, it would override Soviet indignation on the human rights issue under normal circumstances. But what this assessment miscalculated, numerous specialists say, was that the United States made exceptional, not normal, SALT demands at a time of intensified Soviet suspicion.

Vance never even got the opportunity to present the U.S. proposal directly to Brezhnev, as former Secretary of State Henry A. Kissinger did. Instead, it was learned, Brezhnev brushed aside Vance's attempt to make the proposal to him at their first meeting in the Kremlin last Monday, saying he would leave complex technical matters to others.

U.S. negotiators do not know if this was because of the 70-year-old Brezhnev's physical condition or chagrin over the new pattern of U.S. actions. Gromyko, it was observed during the talks, was acting in a more authoritative independent manner than ever before in such meetings.

Vance, who had never met Brezhnev before, was put in the position of making the strongest SALT demands any secretary of state ever put to a Soviet leader, proposing drastic changes in a negotiation that Vance's predecessor, Kissinger had assured the Kremlin was "90 per cent complete."

The Carter administration contends that it is not bound by previous Kissinger proposals, because no agreement was concluded. Additionally, for the quick SALT agreement the Kremlin wants, the United States has offered the Soviet Union nothing on the American weapons that trouble the Kremlin the most, long-range cruise missiles, after the Soviet Union rejected limitations on cruise weapons offered by the Ford administration as inadequate.

To obtain any restriction on these new, potent missiles, the Soviet Union has to negotiate on the Carter administration's "comprehensive package" for substantial arms reductions. The Soviet Union was unprepared as well as unwilling to do so at this time, and three days of Kremlin talks could not conceivably have done more than brush the surface of this complexity, even if the Soviet Union had been interested in it.

With "hard work" and intensive bargaining, the Carter administration maintains, negotiations could be concluded without extensive delay and a result that would leave both nations far better off with fewer weapons, greater nuclear stability, and reduced costs. The logic may be convincing to many American minds, but in Moscow this week it was totally suspect.