Although there has been a noticeable reduction in rancor between the United States and the Soviet Union in recent weeks, the mood here on the eve of Secretary of State Cyrus Vance's arrival for strategic arms limitation talks is one of caution.

Soviet sources, while saying that a number of problems have yet to be resolved, suggest that Kremlin leaders have a slightly positive view that progress can be made here toward a SALT II accord. But no one is talking publicly of a final agreement.

The official Soviet press, which this summer issued several thoughtful assessments of U.S. policy, has been relatively quiet on SALT. Recently, Defense Minister Dmitri Ustinov said in a speech that the Soviet Union had no intention of bargaining away its military might at the diplomats' table. Depending on the way one feels, that can be read as the sort of thing defense ministers are expected to say, or a clear warning to the Americans not to push for all they want in the way of Soviet SALT concessions - or both.

The official Communist Party newspaper Pravda yesterday criticized President Carter for ordering construction of components for neutron warheads. It said Carter's decision showed the Janus-like nature of U.S. arms policy.

"On the one hand they talk in Washington about the desirability of seeking ways to disarmament," Pravda said, "but on the other, steps are being taken in practice leading in the opposite direction."

Several Soviet sources, however, suggest that the Russians fully expected Carter to order the construction of the components, since that is what he had said he would do earlier this year when he declared a moratorium on the warhead building itself.

Although both sides say SALT is too important to be affected by any other bilateral disagreements, the fact is that each country's perceptions at the bargaining table have been altered at times by non-SALT issues. A case in point is Vance's last visit here in April. Ostensibly here to talk SALT. Vance also raised the issues of Soviet repression of human rights activists as well as Soviet military ventures in Africa.

This time, it is said, the Americans come prepared to talk only about SALT. But several Soviet sources suggest that the Kremlin leaders may themselves have some non-SALT matters to discuss.

These would include the Israeli-Egyptian peace accords, which the Soviets bitterly oppose on grounds that they ignore Soviet allies, including the Palestine Liberation Organization. Both Syrian President Hafez Assad and Algerian leader Houari Boumediene have consulted here in the aftermath of the Camp David summit and the Russians have joined them in denouncing the accords. Assad is said to have gotten major new pledges of arms from the Soviets.

Another matter the Soviets are watching closely is the fate of two convicted Soviet spies, Valdik Enger and Rudolf Chernyayev, who were found guilty this month of espionage charges by a New Jersey federal court. They remain free in the personal recognizance of Soviet Ambassador Anatoly Dobrynin pending sentencing Oct. 30.

According to Soviet sources, if the White House genuinely wants better relations with Moscow, Carter will ensure that the two are returned to Russia without imprisonment. These sources say the Soviets showed their good intentions by allowing convicted U.S. businessman Francis J. Crawford to leave here last month after a Moscow court found him guilty of blackmarket currency violations.

Some Western diplomatic sources say that Soviet moves to improve relations are reflected in the fact that Jewish emigration now stands at about 2,000 a month, the highest number since 1973. In addition, they point to some progress in allowing a number of longtime "refused nik" Jews to leave.