Secretary of State Alexander M. Haig Jr. today accused Moscow of engaging in an "unprecedented" level of nuclear weapons testing at the same time it was publicly proclaiming its willingness to control such arms.

Haig, who had just completed two days of talks with Soviet Foreign Minister Andrei A. Gromyko, told a news conference that the United States has assembled evidence showing that Soviet testing activity last week was "significant in scope and integration of activity."

The Soviet activity, he said, included an antisatellite test, launching of two ground-based intercontinental ballistic missiles, launches of a submarine-based missile and a medium-range SS20 missile and two tests of antiballistic missiles.

"Such activity belies by specific actions the words put forth to the world audience here this week," Haig contended, referring to Gromyko's promise in a speech last Tuesday to the U.N. General Assembly's special session on disarmament that the Soviet Union will not use nuclear weapons first in any conflicts with other countries.

Under questioning, Haig conceded that he had not raised the U.S. charges during the 9 1/4 hours of meetings that he held with Gromyko over the past two days. He said much of the information was not available to him while the talks were under way and that it had been analyzed and made ready for release shortly before the start of his news conference.

Saying he thought it was important to get the information out immediately, Haig added: "It shows a level of interest, skill and activity on the part of the Soviets that is a matter of concern."

He refused to give any further details about the Soviet tests, except to say that no nuclear explosions had been involved. He also conceded that there were no indications that the Soviets had violated any international agreements on nuclear weapons testing.

President Reagan had outlined a tough approach to U.S.-Soviet relations in his speech to the disarmament conference Thursday. Haig, in effect, repeated Reagan's challenge for the Soviet Union to demonstrate its desire for improved relations through actions rather than words.

"There is no doubt about President Reagan's desire to put U.S.-Soviet relations on a stable, long-term basis," Haig said. "But this cannot be achieved without a Soviet willingness to conduct its international affairs with responsibility and restraint."

He added: "It's clearly and squarely up to the Soviets to determine what kind of relations they want to have with the United States."

His words continued the hard-line approach toward Moscow that has been evident the past week in such moves as Reagan's tough talk before the U.N. and the president's decision Friday not to ease his ban on the sale by American companies of oil and gas equipment to the Soviet Union.

This hard line appears to be related, at least in part, to the U.S.-Soviet negotiations on strategic arms reductions scheduled to start in Geneva June 29. Washington and Moscow have been engaging in an exchange of proposals aimed at winning the support of world opinion for their respective bargaining positions.

This maneuvering for position undoubtedly was what prompted the Soviet pledge to renounce first use of nuclear weapons. It also caused Reagan in his appearance at the United Nations to repeat a proposal, originally made last month at Eureka College in Illinois, for deep cuts in the ground-based strategic missile arsenals of both countries.

Haig, challenging the Soviet Union to pick up Reagan's proposals and negotiate seriously, called them "a carefully integrated and thought-through approach to arms control." For that reason, he contended, the U.S. plan "stands in sharp contrast to cosmetics" such as the first-use renunciation idea put forward by the Soviets.

The United States and its North Atlantic Treaty Organization allies repeatedly have refused to renounce the West's nuclear first-strike capability because they contend it would make Western Europe vulnerable to attack by conventional Soviet forces.

Haig dodged questions about the possibility of a summit between Reagan and Soviet President Leonid I. Brezhnev by saying that "the president will comment on that in the months ahead."

Although the summit idea originally was put forward by Reagan, senior administration officials are known to have become considerably cooler to that idea and have said privately that a summit does not appear to be in the offing at this time.

Haig repeated the U.S. contention that any summit must be well prepared and offer the likelihood of a positive outcome. The United States and the Soviet Union "agree that summitry for summitry's sake is to be avoided," he said.

Despite the general toughness of his remarks, the secretary characterized his sessions with Gromyko as "full, frank and useful." Noting that this was his third round of talks with Gromyko since the Reagan administration came into office, Haig stressed that such meetings can only benefit understanding between the two superpowers.

In addition to the broad issues of U.S.-Soviet relations and arms control, Haig said he and Gromyko had discussed the full range of global problems in which the two countries have an interest. He refused, however, to elaborate, and said that he and Gromyko had agreed not to discuss the specifics of their conversations on regional problems.

In regard to the crisis in Lebanon, Haig said the Soviets remained "concerned and cautious," but he would go no further in describing possible Soviet responses to the conflict there.

As to the United States, Haig said the administration is continuing to do everything possible to bring about a cease-fire and a long-range solution to the Lebanon situation, but he added that "while these activities are under way, it would be counterproductive to be too specific."