Soviet leader Mikhail Gorbachev and his government are trying to reduce tensions with Japan as part of a new "soft policy" directed at the West, according to Japanese Prime Minister Yasuhiro Nakasone.

"I believe Mr. Gorbachev seeks peace," Nakasone said in an interview, because "the Soviets in both foreign policy and domestic policy have come to a stalemate."

Gorbachev "needs time, needs peace, in order, shall I say, to rehabilitate the Soviet communist system," Nakasone said. He said Gorbachev cannot allow next month's meeting with President Reagan in Geneva to end in failure, but he added that it may take the Soviet leader up to five years to come forward with a "daring or bold compromise with the West."

Nakasone said it is important "for the western camp" that "certain items" be set forth by Reagan "for consideration toward settlement of the issues to be presented at the summit . . . so that dialogue can continue." Nakasone did not elaborate on what he thought the U.S. initiative should be.

The Japanese prime minister, who Thursday attended a "minisummit" with Reagan and other western leaders, made his observations on Tuesday. This part of Nakasone's remarks was embargoed until after his meeting with Reagan this morning.

Nakasone, while welcoming the prospect of improved relations with the Soviet Union, said that for Japan, "the territorial issue . . . cannot be bypassed." The Soviets hold what the Japanese describe as their Northern Territories off Hokkaido. The Kremlin says that these islands are Soviet territory, are not subject to negotiations and will not be returned.

Nonetheless, for the first time in eight years, a Soviet foreign minister -- Eduard Shevardnadze -- has scheduled a trip to Japan, a development that Nakasone says he sees as a signal of a new Soviet approach.

"When Mr. Andrei Gromyko was the foreign minister, he intransigently refused to visit Tokyo even for the regular Japanese-Soviet foreign ministers' meetings," Nakasone said. By putting Shevardnadze in the foreign ministry post, "I believe Gorbachev is trying to . . . change from the rigid, old diplomacy of Gromyko."

He conceded that Gorbachev's "soft policy" toward both Europe and Japan may be an effort to "drive a wedge" into U.S-European and U.S.-Japanese relations. But for his country, Nakasone said that it is necessary to explore the new Soviet initiative to see if it has substance.

"In the sport of judo, for example, if your opponent comes out with a soft-handed approach and you try to overpower him with a hard-handed approach, then you'll be defeated. So it is a basic rule that when the opposite side takes a soft attitude, we also respond with a light attitude," Nakasone said with a smile.

He said Gorbachev, who is about 20 years younger than Gromyko, "has that much time to rectify the numerous deficiencies and shortcomings" in Soviet policy.

"I believe that Gorbachev's intention is to carry out a major innovation or revamping of the Soviet system . . . . He's a man who does not know revolution. He's a post-revolution generation party member and, therefore, behaves more in terms of rationalism and hasn't gotten much of what might be called romanticism. And since he knows Western Europe as well, he probably considers himself a modernist."

If Reagan and Nakasone do their "homework," Nakasone said, their talks "could have some effect of reducing tension and may have good effects on regional conflicts in the Middle East and other parts of the world.