TOKYO, DEC. 12 -- Facing a flood of domestic criticism, the Japanese government has decided that it will send emergency food assistance to help the Soviet Union make it through the winter.

"We have not made it public yet, but the government has decided to take positive steps," said Kazuhiko Togo, a Soviet affairs specialist in the Japanese Foreign Ministry. He said the cabinet had authorized the sending of medical equipment and supplies, food and expert advice to help the Soviets improve their food distribution system.

Togo said the amount of food to be sent had not been determined. The government last week announced that it would send at least $20 million in medical aid.

With food shortages appearing in Moscow and some other parts of the Soviet Union, European nations are already providing emergency aid and the United States is preparing to do so.

The Japanese government has not made any public commitment to provide food assistance to a country with which it has had difficult relations dating back at least to the Russo-Japanese War in 1904. Japan and the Soviet Union have not yet signed a peace treaty formally ending World War II. The two Asian powers have been arguing for 45 years over rights to four islands off Japan's north coast occupied by the Soviets just after the war.

But the Japanese people, reacting to news reports about serious hunger problems in parts of the Soviet Union, seem ready to overlook that history now. As in many Western countries, Soviet President Mikhail Gorbachev is extremely popular here, and his personal magnetism is helping overcome the traditional hostility toward the Soviets. There had been intensive media criticism here of Prime Minister Toshiki Kaifu's government for delaying emergency aid.

"Why can't Japan even try to help Gorbachev?" asks a poster in the Tokyo subways this week. The poster is advertising a scathing article in the weekly magazine Sunday Mainichi that excoriates Kaifu and the government for delaying while European governments have been quick to help.

Japan's private sector, which is normally inclined to wait for government leadership on international affairs, has begun to respond to the Soviets' difficulty while the government remains silent.

Japanese food companies are planning to ship a range of foods, from powdered milk to instant ramen noodle soup, to Soviet food distribution points. So many organizations are gathering private contributions to aid the food drive that the government has set up an office to coordinate the private efforts. The government of Kawasaki, a Tokyo suburb, already has dispatched a planeload of donated supplies to Moscow.