Secretary of State Cyrus Vance reported to President Carter yesterday that one obstacle to a new U.S.-Soviet nuclear arms pact was overcome in Moscow but too many others remain to forecast when an accord might be capped at a summit conference.

Administration sources confirmed that the United States would be free to transfer cruise missile technology to its Western European allies under terms projected in Vance's talks in Moscow.

The North Atlantic Treaty Organization council in Brussels was informed yesterday of this advance, to allay concern that America's allies would be deprived of the long-range, jet-powered weapons, similar to a pilotless drone aircraft. President Carter had pledged that no new strategic arms limitation treaty would be signed unless the Soviet Union relented on trying to bar cruise missiles to U.S. allies.

In accord with the Carter administration's new efforts to avoid arousing expectations that can collapse, officials made no attempt to trumpet the marginal gain.

Vance returned from a 12-day, 25,300-mile mission to Africa and Europe bringing a mixture of limited advances and several disappointments, with no one venturing to put a high gloss on the outcome.

Vance, at Andrews Air Force Base and later at the White House after reporting to the president, spoke of "some forward movement" and "further hard work." He declined even to tie himself to a claim that a new nuclear accord will be completed this year, although Carter often has done so in the past.

The discussions that Vance had in Moscow appear to have mitigated - but not to have wiped out - Soviet leader Leonid Brezhnev's charges earlier this month that the Carter administration is indecisive and vacillating.

When the U.S. delegation left Moscow on Sunday, Moscow-based Communist reporters were being told that the Soviet Union was "somewhat disappointed" by the negotiating proposals that Vance brought with him. In addition, Soviet diplomatic sources said they still had doubts about the ability of the Carter administration to move forward rapidly to complete the prolonged negotiations.

With this posture, the Soviet Union gains the psychological and propaganda advantage of claiming, as it is doing, that Soviet "constructive position" is the driving force in the negotiations.

At the same time, the Carter administration has turned to an extremely guarded position on disclosing what took place in the meetings between Vance and Brezhnev, Soviet Foreign Minister Andrei A. Gromyko and other Soviet officials.

Vance told reporters at the White House, "the mark of the seriousness of the negotiations is the secrecy surrounding them. If we get into the open it is regarded as a propaganda exercise by them."

The Carter administration started with just the opposite premise, of "open diplomacy." Its original reach for "a bold leap forward" in nuclear arms control a year ago, as officials recalled it yesterday, however, was over-ambitious and badly coordinated, landing the administration in a bitter crossfire of recriminations with the Soviet Union. In Moscow on his departure Sunday, Vance used the reverse metaphor, speaking of a "brick-by-brick" approach.

Now the Brezhnev-Vance talks indicate that the Soviet Union, as the United States wants to "cool the rhetoric," reporters were informed. Brezhnev is expected to make a speech in the Soviet Union today that could include comment on the Vance trip.