Japan-Soviet relations are on the mend. At least both sides are showing signs that they want to improve them. A delegation of senior Soviet parliamentarians has just left Japan after a week-long visit at the invitation of members of Japan's Diet (parliament). The mission, headed by Politburo member Dinmukhammed Kunayev, was the first visit by a senior Soviet official to Japan since Foreign Minister Andrei Gromyko's visit in 1976.
Mr. Kunayev met Prime Minister Yasuhiro Nakasone, Foreign Minister Shintaro Abe, Diet members, and industrial representatives. The Soviets sought to narrow differences and promote closer ties.
The Japanese welcomed these overtures. Although the meetings did not lead to any concrete results, political analysts say they will contribute to bettering Japan-Soviet ties. Many note that the Soviets appear to be adopting a softer diplomacy toward Japan.
At a press conference, Soviet spokesman Vadim Zagladin said the two countries have started a ''process of narrowing their differences.'' Mr. Zagladin also hinted that Mr. Gromyko may pay another visit to Japan.
Japan has been asking Gromyko to visit Tokyo for regular consultations, but the latter had been reported unwilling to come unless Japan dropped discussion of the northern territory issue.
The soft Soviet diplomacy follows a year that has probably seen the lowest point in Japan-Soviet relations.
Ties between the two countries have been strained since the end of World War II, when the Soviet Union annexed four northern islands off the coast of Hokkaido.
Relations deteriorated after the invasion of Afghanistan, when Japan followed Western countries in imposing economic sanctions against Moscow. And anti-Soviet sentiments were fueled by the downing of the Korean Air Lines jet last September and reports of a Soviet military buildup in the Far East.
For Japan the newly amicable mood comes at the right time: Since Mr. Nakasone took office two years ago, he has made a number of diplomatic trips to major countries - except the Soviet Union.
The Japanese government has made a few attempts to establish contact with the Kremlin leaders. Foreign Minister Abe met with Gromyko in Moscow last February at the funeral of Yuri Andropov, and again at the United Nations in New York last September. Other Japanese delegates have visited Moscow in recent months.
Soviet-watchers point to a number of reasons why Moscow should soften its approach toward Japan.
* The USSR needs funds to get its new economic development plan, which starts in 1986, off the ground.
Japan has been involved in major development projects in Siberia, but since the Afghan sanctions, it has been less forthcoming in its involvement. After five years, the two nations are resuming Business Cooperation Committee meetings in December. By improving relations before that, the Soviets hope they'll get Japanese commitment for economic cooperation, observers say.
The Soviets are counting on Japanese expertise in high technology now that the US is trying to restrict these exports to communist countries.
* Establishing harmonious relations with Japan might help improve ties with the US.
* Much has been going on in the Asian region: North Korea has been signaling it wants to open up to the West, as has China. Soviet watchers say Moscow probably doesn't want to be left out of this trend.
Japan also used this visit to reassure the Soviet Union of its intention not to become a military power.
The Japanese leaders made a point of insisting that Japanese-Soviet relations can't be improved until the northern territorial issue is settled.