Soviet leader Mikhail Gorbachev warned today that the arms talks in Geneva would collapse if the Reagan administration continued its present negotiating policy.

In a nationally televised speech, Gorbachev said an agreement in Geneva was possible if the United States "ventured to take a more reasonable stand."

"But if our partners in the Geneva talks carry on their line, marking time at the sessions of the delegations, avoiding solutions to the problems for the sake of which they have gathered, and using that time to intensify their programs of arms buildup -- in space, on the land and on the seas -- we, of course, will have to reassess the entire situation," Gorbachev said.

"We just cannot allow the talks to be used anew as a decoy, as a cover, for military preparations, the purpose of which is to ensure the strategic superiority of the United States and its course of achieving world dominance," he said.

It was the strongest statement by a Soviet leader on the Geneva talks since they resumed in March. Gorbachev denounced the Reagan administration's "militarist policy" for which, he said, the United States "is incurring a grave responsibility to mankind."

He said that Washington had made no serious proposals at Geneva. "The Americans, conversely, are taking steps which are making this process impossible," he added.

Gorbachev specifically singled out President Reagan's Strategic Defense Initiative, which Gorbachev asserted involved "the development of attack space weapons."

"Talk about its alleged defensive character is, of course, a fairy tale for the naive," he said. "The plan is to try to neutralize Soviet strategic weapons and to secure a possibility to deliver with impunity a nuclear strike at our country.

"This is the crux of the matter and we cannot help but bear this in mind. The Soviet Union, if it faces a real threat from space, will find effective means to counter it -- and I can say quite definitely that no one should have any doubts about it. So far, it is only clear that the U.S. program to militarize space is like a blind wall blocking the way to agreements in Geneva," Gorbachev said.

Gorbachev's statement that Moscow could not allow the Geneva talks to be "used anew as a decoy" for Washington's military buildup clearly linked his warning to a similar statement issued by the late Soviet leader Yuri Andropov in 1983. Andropov said at the time that the talks would become impossible if the United States started its planned deployment of medium-range nuclear arms in Western Europe. The Russians walked out of the Geneva talks in late 1983 when the first Pershing II missiles arrived in West Germany.

The Soviet leader was speaking to metalworkers in the Ukrainian city of Dnepropetrovsk. He is currently on a tour of the Ukraine, mobilizing support for his economic modernization program.

Gorbachev also spoke on other foreign policy matters, expressing cautious satisfaction with the course of Soviet-Chinese relations.

"I think time has shown to both sides that neither stands to gain from discords, let alone unfriendliness and suspicion, and that good neighborly cooperation is quite possible and desirable," he said.

"We, for our part, are going to contribute energetically to the complete removal of the negative period in Soviet-Chinese relations, which has produced quite a few artificial overlayers," he said.

The bulk of Gorbachev's speech was devoted to Soviet internal issues. Referring to Moscow's new insistence on labor discipline and its anti-alcoholism campaign, he suddenly asked his audience, jokingly, "Are we tightening up too much?"

A single voice responded by yelling, "No, you are doing the right thing."

"Is this one voice or the general opinion here?" Gorbachev asked, to be interrupted by shouts of approval and applause.