Secretary of State George P. Shultz called on the Soviet Union yesterday to undertake "concrete deeds," including progress in the nuclear test-ban area mentioned last month by Soviet President Konstantin U. Chernenko, in order to start momentum toward improved superpower relations in the second Reagan administration.

In an interview, Shultz said, "Now is the time to push the negotiating and talking" aspects to move beyond the sharp antagonism that has characterized U.S.-Soviet relations for four years. He portrayed President Reagan and the U.S. government as ready and willing but placed the onus on Moscow to take the next step.

Some of Shultz's comments, on the afternoon after Reagan's election victory, seemed to respond to Chernenko's statements in an interview with The Washington Post three weeks ago. At that time, the Soviet leader asked for "real deeds" by Washington in any of four areas of special concern as evidence of sincerity in pursuit of improved ties.

One of Chernenko's four points was ratification of treaties limiting underground nuclear testing. The pacts were concluded by the superpowers in 1974 and 1976 but have never been ratified by the Senate.

Yesterday, Shultz listed three steps that the Soviets might take to start the ball rolling. One is acceptance of the exchange of visits by experts to each other's nuclear-test sites in order to measure directly the size of atomic-test explosions.

Reagan proposed this in his speech to the United Nations Sept. 24 and in a meeting at the White House a week later with Soviet Foreign Minister Andrei A. Gromyko.

Shultz noted in the interview that nuclear testing was one area mentioned by Chernenko last month and that an exchange of experts could be related to the treaty ratification being sought by the Soviet leader.

This is because the United States considers that verification of the size of test explosions, an inexact operation without on-site experience, is the crucial barrier to ratification of the decade-old treaties and agreement on new, more sweeping agreements.

The U.S. proposal calls for the exchange of experts by next spring. Shultz explained that this timetable arises from a U.S. plan for a major underground test at that time.

The two sides' test-ban proposals are known to have figured in the private diplomatic dialogue between senior U.S. and Soviet diplomats here and in Moscow since Gromyko's visit. However, Shultz did not report progress on the issue, saying the U.S. bid for an exchange of experts is "lying on the table, basically."

In the interview, Shultz made two other suggestions for Soviet "concrete deeds": Soviet accord on U.S. proposals submitted at the Conference on Disarmament in Europe (CDE), initiated last January by Shultz, Gromyko and ministers of 33 other nations.

Shultz cited "some progress" toward a meeting of minds in this forum, including a private visit by the senior U.S. negotiator to Moscow and that of his Soviet counterpart to Washington. But he said substantive agreements remcin to be forged. A start on "the major issues of arms control," which include offensive and defensive nuclear missiles.

Shultz seemed to reject again the Soviet demand for agreement on a moratorium on space-weapons testing, effective at the start of the talks, saying, "I don't think you start with something that gets agreed to before you begin to talk." He added, though, "there are a variety of ways to get discussions going."

Reagan told a Los Angeles news conference yesterday that he had discussed with the Soviets the establishment of "a separate informal channel" to promote major negotiations.

Asked about this, Shultz said Reagan is striving to "create a setting" in which "high-level and political people" in the two governments can exchange views. Having held lengthy discussions with Gromyko, Reagan would like to see "more of the same" between Gromyko and Shultz and between the ambassadors and foreign ministers in the two capitals, Shultz said.

Weighing his words carefully, he added, "It may be that as part of this, in some emphasis on a particular topic or other, it may be desirable for a person who is going to spend all of his time on a particular subject to be there, a subject like arms control."

That was as close as Shultz came to endorsing the idea of naming an administration arms-control "czar" with the task of organizing and presenting U.S. positions in that important field.

He said a "czar" implies "somebody who is going to sit somewhere and run everything" away from other actors in the government. "I don't think that kind of idea works," he added.

Regarding his future, Shultz declined to say whether he will remain secretary of state if asked to do so by Reagan. He said this is a subject that he must discuss with the president, with whom he has had only a brief telephone exchange since the election.

In nearly the next breath, he reported, "I'm working very hard on what I think is a good agenda for the time ahead."

Asked if the United States is prepared to undertake a more direct and intensive role in negotiations regarding Israel's withdrawal from Lebanon, Shultz replied that "we're playing a very considerable role" through the current mission in that area by Assistant Secretary of State Richard W. Murphy.

After Murphy returns in the next week or so from visits in Israel, Lebanon, Syria and elsewhere, the administration will "take stock" of the question of a more prominent role than the "helpful" and "quiet" one already under way, Shultz said.