After months of delay, plans for the next superpower summit appeared to move forward yesterday as departing Soviet Amabassador Anatoliy Dobrynin told President Reagan that Moscow is ready to schedule a high-level preparatory meeting next month and assured him the Soviets are not setting conditions for the summit. Secretary of State George P. Shultz announced afterward that he would meet Soviet Foreign Mnister Eduard Shevardnadze in mid-May to begin what he called "a major push" toward the summit, although a date has not been set. Reagan told aides yesterday that he still prefers a summer summit, in June or July, but other officials said June may be out of the question at this late date, and if the Soviets balk at a summer meeting, November could be an alternative. Shultz said, "I wouldn't rule anything in or out." Dobrynin brought Reagan a letter from Soviet leader Mikhail Gorbachev expressing a desire for "concrete agreements" to come out of the next summitt and indicating that Gorbachev is "still serious about maintaining a dialogue" began at their meeting in Geneva, officials said. In Moscow, Gorbachev declared in a speech that he wanted to make it "absolutely clear" he favored another summit meeting with Reagan and made "no preconditions for it," but he struck a stern note as he laid out the prospects for improving U.S.-Soviet relations. Reagan's planned 15-minute farewell to Dobrynin stretched into a 75-minute session that Shultz said touched on "all the issues of substance" between Washington and Moscow. Administration officials said the president, while discussing "flashpoints" around the globe, brought up U.S. concern about Libyan sponsorship of terrorism and Soviet military support for the regime of Libyan leader Muammar Qaddafi. Shultz, who was at the Oval Office meeting along with other top Reagan advisers, said both nations "wish to see a successful and substantive" summit that shoud have "something significant connected with it. Both parties agree on that. Beyond that ther are no particular preconditions." The Reagan meeting with Dobrynin came as the United States postponed a nuclear test for what officials said were technical reasons unrelated to the summit. The test, when carried out is expected to trigger the end of Gorbachev's self-imposed moratorium on nuclear testing. Shultz said nuclear testing was one of the topics discussed yesterday, but he did not provide details. Shultz said the meetng did not leave U.S. officials with the impression that the Soviets were prepared to accelerate movement on arms control issues in Geneva. he said "there has been basically no movement" in talks on limitingg strategic weapons, and "there has been basically no movement in the space defense area." On intermediate-range weapons in Europe, Shultz said the exchange of proposals recently has resulted in a "further narrowing of positions." He cited progress in bilateral issues such as cultural exchanges, civi aviation and consulates. But he also said, without being specific, there has been "increasing strain" in other areas of U.S.-Soviet relations. Shultz described the meeting with Dobrynin, who is leaving the United States to become chief of the international department of the Soviett Communist Party Central Committee, as "very substantive" and "constructive" and said it "advanced matters." Other officials, who had been concerned about summit prospects, expressed relief that the meeting seemed to move the planning ahead. As a farewll gift, Dobrynin had earlier presented Reagan with an electric samovar and nine china figurines.