Instead of borscht and blini, Soviet officials have taken to tantalizing their palates with tempura, sushi, sukiyaki and the like.

The Japanese restaurant Sakura, the most expensive and exclusive in the Soviet capital, has replaced the assorted mixture of Czech, Georgian and Russian restaurants as many Soviet bureaucrats' top choice for a business lunch with diplomats or journalists.

In this capital, where protocol and national pride run high, where American hamburgers, German sausages and English pork pie are hard to find, the new-found taste for Japanese cuisine may be the most visible expression of a gradual upturn in Japanese-Soviet relations that has come about since Soviet leader Mikhail Gorbachev came to power last March.

After five years of cool relations, Japan and the Soviet Union are going through a thaw, diplomats from both countries acknowledge. For the first time in a decade, the Soviet foreign minister is planning a trip to Tokyo.

Following a three-year decline, Japanese businessmen here expect a slight upswing in this year's $4 billion trade between the two countries. Since September, the Kremlin has softened its long-running attacks against Japanese Prime Minister Yasuhiro Nakasone's government and launched an appeal for improved links between the two countries.

So far, western and Asian diplomats here say, the improved atmosphere has done little to camouflage the longstanding dispute between Moscow and Tokyo over the northern territories, the four Kurile Islands that the Soviet Union took from Japan at the end of World War II.

Japanese diplomats in the Soviet capital have reiterated Tokyo's position that return of the islands is a prerequisite for a peace treaty with Moscow and for long-term improvement of Soviet-Japanese relations.

But as Soviet Foreign Minister Eduard Shevardnadze's Jan. 15-20 visit to Japan approaches, the Kremlin has stressed other means of strengthening Soviet-Japanese ties, including increased economic cooperation, upgraded bilateral ties and Japanese participation in an all-Asian forum.

"We stand for better relations with Japan," Gorbachev told Supreme Soviet delegates in a major speech late last month, "and it is our conviction that this is possible."

The Soviet leader's expression of good will is far from the Kremlin's traditional hard-line Japanese policy. In a 1982 meeting often recalled by Japanese diplomats here, a Soviet official summed up the policy in one word: "intimidation."

Last year, Moscow's war of words against Japan reached a deafening pitch in a media campaign commemorating World War II, which dramatized Japanese "militarism" and "revanchism" and continuously reminded Soviet citizens of Japan's involvement against the Soviet Union in the war.

Western diplomats here consider the Kremlin's overtures toward Tokyo the clearest example of Gorbachev's foreign policy, which is more varied, multidirectional and dynamic than the policy fashioned under former foreign minister Andrei Gromyko, they say. Gromyko never ranked Japan any higher than a third-rate power, diplomats say. In 28 years as foreign minister, he visited Tokyo only three times.

Gorbachev apparently has brought to the Kremlin a higher assessment of Japan's economic and military stature. In the revision of the Communist Party's 1961 program, released in late October, Japan was listed for the first time alongside the United States and Western Europe as a center of capitalist imperialism.

Japan's defense initiatives under Prime Minister Nakasone also have attracted attention in the Kremlin, according to Soviet officials.

Mounting tensions between Tokyo and Washington over Japan's restrictive trade barriers have created an opportunity for the Kremlin to curry favor with the Japanese, they say. Improved relations with Japan, China and other Asian countries are part of an overall strategy to counter U.S. influence in the region, according to their analysis.

During Kremlin meetings with various visitors from Tokyo in recent weeks, Soviet officials have emphasized their opposition to President Reagan's Strategic Defense Initiative. Tokyo has not announced a decision yet about its participation in the space defense research program.

Although Japanese-Soviet trade has slipped after a 1982 high, it remains active, dominated by a $500 million coal development project in southern Yakut, a $1.5 billion lumber development venture in southern Siberia, and Japanese involvement in two major petrochemical consortiums with several Western European countries.