Mikhail S. Gorbachev and President Reagan concluded four days of summit talks Wednesday with an impasse on a major arms control agreement and differences on human rights. Nevertheless, the Soviet leader called their meetings "a blow to the foundations of the Cold War" and Reagan said "we must not stop here."

Once they exchanged smiles and handshakes, the two leaders held separate news conferences, an unusual event for Reagan but an unprecedented episode for Gorbachev on his home soil.

The Soviet leader took pleasure that Reagan had disavowed his description of the Soviet Union as an "evil empire." He noted with satisfaction that Reagan did it "within the walls of the Kremlin."

Gorbachev said that when Reagan tried to move him on human rights, "I said, `your explanations are not convincing.'" The Soviet leader said he also told Reagan his view of the "Star Wars" program as a strictly defensive system was "just not serious."

Reagan, in turn, muted his criticism of the Soviet system; he hailed Gorbachev's moves to open up his country's society and suggested that Soviet refusal to permit thousands of dissidents to emigrate over a period of several decades might be due merely to an unresponsive bureaucracy.

Asked at a news conference if he was letting Gorbachev off too easy, Reagan replied, "I just have to believe that in any sort of government some of us do find ourselves bound in by bureaucracy."

His comment raised eyebrows among refuseniks in Moscow.

"I think he's naive about that," said Abe Stolar. "Maybe that's a bad word to use, maybe it's just innocent."

Another refusenik, Tanya Zieman, also disagreed with Reagan's explanation but said that perhaps Reagan "just didn't want to anger our side more. My feeling is as if some agreement is reached and he does not want to hamper it by saying nasty things."

Reagan and Gorbachev both vowed to persist in efforts to negotiate a new treaty calling for sweeping reductions in nuclear weapons despite their inability to achieve a breakthrough in four days in Moscow.

The president said he hopes for an arms control agreement by the end of his term in January to supplement the INF treaty that was formally ratified during his four days in Russia. But, he quickly added, "I am dead set against deadlines."

"We can look with optimism on future negotiations," he said, even though he continued to defend his proposal for "Star Wars," which has been a key stumbling block in superpower arms-control negotiations.

On arms control, a joint communique said the two sides had made progress - but not solved - some of the thorny problems associated with cruise missiles fired from warplanes, and the monitoring of elusive mobile missiles. U.S. arms negotiator Edward Rowny said there was "a lot of room" to go in the two areas.

Moreover, he said "we didn't get anywhere" on perhaps the two biggest obstacles to a treaty: keeping track of submarine-fired cruise missiles and Soviet objections to Reagan's missile-defense program, popularly known as "Star Wars."

The communique said "serious differences" had emerged on the causes and solutions to regional tensions, but that the superpowers would try to improve their relations, anyhow.

It was Reagan's decision to softpedal differences on human rights that seemed likely to be his most memorable comments at a news conference televised live in the United States - particularly after his meeting two days earlier with dissidents who told him personally of their imprisonment and internment in labor camps during their struggle to emigrate.

The leaders ended their fourth summit by exchanging the documents of ratification of the intermediate-range nuclear arms treaty (INF) signed last December. They said they will press to complete an elusive agreement to cut strategic nuclear weapons by up to 50 percent.

"The first lines have already been written into a book of the world without nuclear weapons," Gorbachev said. ". . . I don't think anyone can close that book and put it aside."

In his news conference - the first such session ever held by a Soviet leader in Moscow - Gorbachev said the president's Strategic Defense Initiative remained as one key obstacle to an offensive arms agreement, along with a dispute over limits on submarine-launched cruise missiles.

In remarks to reporters, Gorbachev generally praised Reagan although he said American economic and arms policies were often contradictory.

Gorbachev summarized their meetings as "big politics, politics that affect millions of millions of people." He said that with the INF treaty, "the era of nuclear disarmament has begun."

Reagan, praising the INF treaty as historic because it mandates the elimination of an entire class of nuclear weapons, said, "We must not stop here, Mr. General Secretary. There is much more to be done."

Despite the lack of major agreements, it was an upbeat windup to the fourth summit in 30 months between the two leaders and the first visit to Moscow by an American president in 14 years.

Gorbachev made a point of noting that Reagan had said he no longer viewed the Soviet Union as an "evil empire." Reagan said Tuesday he had been talking about "another time, another era."

In the absence in a strategic arms pact, Gorbachev said "we will not make any dramatic conclusions" at this summit. However, he said, they were moving "step by step" toward an eventual treaty.