The Carter Administration and the Soviet, Union today presented fundamentally conflicting positions on nuclear-arms control and human rights in their first encounter at the Kremlin.

Soviet Communist Party leader Leonid Brezhnev cautioned Secretary of State Cyrus R. Vance this morning that unless the United States accepts the principle of "non-interference in internal affairs," the search for constructive relations "is impossible."

Brezhnev then did not appear at the afternoon talks, where Vance made the major U.S. proposal of his Moscow visit, to press now for "deep cuts" in both countries' nuclear arsenals.

Brezhnev's stern warning about the risks of the Carter administration's policy on human rights was essentially a repetition of his March 21 indictment of "Washington's claims to teach others how to live." But the fact that Brezhnev pursued the issue so determinedly at his first meeting with Vance, and that Soviet Foreign Minister Andrei Gromyko then reiterated it at a luncheon, made that theme the dominant Soviet message today.

In response to the American priority for sharp acceleration of negotiations to limit intercontinental nuclear weapons, the Soviet Union countered by holding firm on the essentials of its past proposals.

At the end of an obviously wearying day, Vance tonight sought to head off quick judgments on the outcome of his mission.

In sketchily summarizing the day's events for reporters, avoiding disclosure of the U.S. plan or the Soviet counter proposal, Vance said he would not characterize the situation "as optimistic or pessimistic."

What is significant," Vance said, is "we are talking," and he said the Soviets are now studying the admittedly complex American offer, Vance called the atmosphere of the day's meetings "businesslike" - a diplomatic terminology for blunt, but correct, and inconclusive exchanges.

He said that Brezhnev's statement had the effect of "clearing the air." Referring to the controversy over human rights, Vance said hopefully, "I suspect that it is over with" for the remainder of his talks here.

The secretary said he repeated to Brezhnev that "our human rights issue springs out of fundamental values," which are very different in the two societies, that the United States is not simply singling out the Soviet Union for criticism, but that "we will continue to do what is necessary" to uphold American values.

Today's significant exception to the emphasis on U.S.-Soviet differences was a seemingly important shift in the Soviet position on Palestinian participation in a reconvened Geneva conference on the Arab-Israeli dispute.

Gromyko, in a departure from the prepared text of his luncheon toast, asked: "Can't we decide on [Palestinian] participation at the conference itself?"

Until now the Soviet Union has maintained that the Palestinian Liberation Organization must be represented from the outset of the conference, for which the United States and the Soviet Union would be co-chairmen, Israel has adamantly opposed that demand.

The elliptical manner in which Gromyko raised the possible breakthrough on this issue aroused both high interest and uncertainly on the U.S. side. The Soviet Union has been extremely eager to recapture a major role in Arab-Israeli diplomacy. In his major speech March 21, Brezhnev had also indicated potential new Soviet flexibility on a Middle East peace formula.

Asked to assess the import of Gromyko's move, Vance said, "What he meant by that I am not sure." Vance said the matter would be explored in further talks here.

Gromyko's apparent gesture on the Middle East underscored the dual posture the Kremlin is taking in these first, testing, top-level talks with the Carter administration.

On the one hand, Moscow is expressing fierce opposition to what it sees as intolerable U.S. encouragement for internal challengers of its rule. On the other hand, the Soviets are holding out tempting prospects for greater U.S.-Soviet cooperation if the Carter administration will back off on the human-rights issue and also help fulfill Soviet aims in strategic arms talks, trade and other areas.

The talks began this morning in the Kremlin with the softer side of this posture on public display. Brezhnev, meeting Vance for the first time, was quite amiable with Soviet cameramen present.

In a tangle of their own with Soviet authorities, the American reporters declined to attend because of what they regarded as restrictive limitations compared to past such meetings. Soviet officials later expressed regrets and sought to make amends.

According to the American delegation spokesman, Brezhnev, exchanged pleasantries with Vance, who celebrated his 60th birthday in Moscow yesterday with a cake baked by his wife. Brezhnev also asked Vance to convey "my heartfelt good wishes" to President Carter. State Department spokesman Hodding Carter described the brief public prelude as "a cordial atmosphere, dominated by small talk," adding, "I think it was very warm."

The Soviet news agency, Tass, reported that Brezhnev's closed-door comments on "fundamental questions of Soviet-American relations" stressed hopes for "steadily advancing on the basis of the progress reached in Soviet American relations in previous years." It added this firm caveat:

At the same time an appropriate appraisal was given (by Brezhnev) on those moments in the U.S. policy which do not square with the principles of equality, noninterference in the internal affairs of each other and mutual benefit, without the observnce of which the constructive development of relations between the two nations is impossible."

Soviet television tonight briefly displayed the first moments of the Brezhnev-Vance meeting, following by a reading of the Tass report.

The opening meeting this morning with Brezhnev present lasted 2 1/2 hours. Vance described it as an "exchange of views and then a dialogue" on overall U.S.-Soviet relations that included Vance's rebuttal to Brezhnev on Carter administration human-rights policy.

At the lunch given by the Soviets, Vance said in referring to the morning session that "We agreed that at the heart of these discussions lies the question of reducing the threat of war and of curbing the arms race."

Vance made no reference to Brezhnev's warning on U.S. human-rights policy, nor to Gromyko's assertion that it would be a "serious mistake" for the United States to fail to recognize the "signal importance" the Soviet Union attaches to the principles of "equality, noninterference in internal affairs and mutual benefit."

On nuclear-arms control, Gromyko said, "It is of central importance that we do not reject what has already been achieved but that we build on it. Here we mean specifially the Vladivostok understanding, which is an international agreement between states reached at the highest level."

It was not until the evening meeting that Vance laid out the U.S. nuclear proposals, at what he described tonight as "considerable length."

Vance told reporters he did not regard Brezhnev's absence as "significant." Former Secretary of State Henry A. Kissinger always sought to make important SALT proposals directly to Brezhnev.

The American formula seeks major reductions in strategic nuclear launchers by cuts significantly below the 2,400 strategic missiles or bombers on each side outlined at Vladivostok in 1974 by Brezhnev and former President Ford.