The long-awaited talks between the United States and Soviet Union on reducing nuclear weapons in Europe got off to what appeared to be a good start here today, with a Soviet spokesman describing this first meeting as "very constructive" and with chief U.S. negotiator Paul H. Nitze understood to have been very satisfied by his first encounter with the Soviet delegation chief, Yuli Kvitsinsky.

The two men met privately at the Soviet mission here for 90 minutes with only translators present and afterward Nitze made it clear that because of the importance they attach to the talks, both delegations would attempt to impose a virtual news blackout on details of them, at least for a while.

In a statement he read to reporters, Nitze said both sides "have concurred that the details of the negotiations must be kept inside the negotiating rooms."

Since "the stakes are very high for all of us" and since "we want these talks to succeed," Nitze said, "we will not discuss publicly the issues on the negotiating table."

He said that "it is only by mutual respect for the confidentiality of these procedings that we can hope to look at the hard issues which divide us and to search for solutions that will assure security and reduce tensions."

Today's private meeting was largely procedural, with much of the time taken up by the question of how to deal with the press and with other "broader issues," according to a U.S. spokesman, Joseph Lehman. The first session involving the full delegations of both sides is to take place tomorrow.

It was learned, however, that Nitze was pleased by the atmosphere at today's meeting and that, while no formal proposals were put forward by either side, there was said to be a feeling, at least on the U.S. side, of a consensus with the Soviet chief on the approach to the negotiations.

It was understood that there was reason to believe that neither side would confront the other with an ultimatum, that the negotiations would proceed in good faith and that no early breakdown was likely.

A Soviet spokesman, Vladimir Evdokuchin, described today's meeting as "very constructive, with both sides striving toward agreement." He said it was too early to comment on any substantive issues and that Kvitsinsky also had no immediate plans to comment.

The approach of these negotiations, which will deal with eliminating or reducing intermediate-range nuclear missiles and possibly bombers based in Europe, has attracted extraordinary attention in Europe as well as in Washington and Moscow.

The West European press and television has been dominated for days by speculation about how these talks might go and what success or failure would mean for stability in Europe and for chances of war between the superpowers that might be fought on a European battlefield.

In part, that is why so much attention in this first session was apparently devoted to figuring out what to say in public. Sources here said privately that both sides acknowledged that public expectations are running high, that the situation is volatile and that both sides would be vulnerable to attempts to take advantage of the situation through one-sided public comments.

In addition, the choice of Kvitsinsky to head the Soviet delegation is one that sparked some concern initially among U.S. officials. He is a skilled diplomat who served as the deputy ambassador in Bonn, speaks flawless German and maintains excellent contacts with many politicians from West Germany, the key Western nation in the allied plan to bolster missile strength if no arms agreement can be reached.

There was concern that Kvitsinsky might prove to be a weapon for the Soviet side if the rules for public appearances and statements were too loose. Now, however, both U.S. and West German sources say they doubt that Moscow would weaken Kvitsinsky's effectiveness in the talks by using him as a propagandist.

On Nov. 18, President Reagan laid out the U.S. approach to these negotiations. He offered to forgo planned deployment in Western Europe of 572 new U.S. Pershing II and cruise missiles, scheduled to be fielded beginning in 1983, if the Soviets will dismantle some 600 intermediate-range missiles already in the field that are able to hit Western Europe.

The Soviets have basically rejected this so-called "zero option" offer and Soviet President Leonid Brezhnev has talked instead of a moratorium on adding new missiles while negotiations proceed. As an inducement, he also offered to make advance reductions of "hundreds" of such weapons.

Brezhnev did not say specifically what kinds of weapons he was talking about or on what terms. Later, his spokesmen also talked of "complete renunciation by both sides" of all medium-range nuclear weapons in Europe.

The West rejects a moratorium because it would leave the Soviet advantage in place. Talk of a complete ban on such weapons is thought to be a Soviet attempt to get the British and French nuclear forces plus hundreds of U.S. and allied warplanes based in Europe into the negotiations.

The United States also wants these talks to be held in phases, with the first effort devoted to the main threat posed by missiles such as the Soviet SS20 that can fly some 3,000 miles.

While there was no indication of discussion on this issue here today, West German Chancellor Helmut Schmidt suggested in an interview in the West German magazine Der Spiegel that such a plan would work.

As a result of his recent talks with Brezhnev in Bonn, Schmidt is quoted as saying he could "very well imagine that one could meet a consensus in the first phase of negotiations on a solution to the missile problem if, at the same time, there was an agreement in principle on the subsequent phase in which the remaining medium-range weapons would be brought into the balance."

Nitze also announced the other members of the U.S. delegation.

Maynard W. Glitman, a former top official at NATO, is Nitze's deputy. Others include John A. Woodworth from the office of the secretary of defense, Gen. William F. Burns from the Joint Chiefs of Staff and two officials of the Arms Control and Disarmament Agency, Thomas Graham Jr. and Norman G. Clyne.

Washington Post correspondent Dusko Doder reported from Moscow:

The Soviet leadership voiced readiness tonight to open a political dialogue with the Reagan administration and urged it to give "full and objective consideration" to Soviet proposals on curbing nuclear arms in Europe.

A joint statement by the ruling Politburo, the government and the presidium of the Soviet parliament on the opening day of talks in Geneva seemed designed to show the Western Europeans that the Kremlin is serious about the talks and that it has serious doubts about U.S. intentions to seek a "mutually acceptable agreement" but that in the course of the talks Western Europe's governments and public could play an important role.

The statement, distributed by the official news agency Tass, said planned deployment of new U.S. medium-range nuclear weapons in Europe was the "most acute and burning issue" and that it would tip the balance of forces in favor of the West.

It restated Brezhnev's proposals made in Bonn, including the assertion that "of course" U.S. European-based warplanes and British and French nuclear weapons would have to be included in the talks.

"It is expected in the Soviet Union that the West, above all the United States, will give full and objective consideration to the fresh Soviet initiatives," the statement said.

[Meanwhile, in a broadcast to Western Europe, Secretary of State Alexander M. Haig Jr. said eventual success in the Geneva talks depends on NATO's continued resolve to move ahead on its program to produce and deploy those weapons, United Press International reported.]

[These preparations are the incentive that brought the Soviets to the negotiations and that will encourage them now to take a serious position," Haig said.]