UNITED NATIONS, SEPT. 30 -- The Soviet Union today went against the wishes of its long-time ally, Communist North Korea, and established full diplomatic relations with South Korea, shedding yet another of its Cold War antagonisms.

In a similar step, the Soviet Union and Israel agreed to continue improving their ties by opening consulates general in each other's countries for the first time in the 23 years since Moscow broke relations with the Jewish state following the 1967 Middle East war.

The actions were announced after Soviet Foreign Minister Eduard Shevardnadze held separate meetings here with his counterparts from South Korea, Choi Ho Joong, and Israel, David Levy.

"We have agreed to establish diplomatic relations between the Soviet Union and South Korea as of today," Choi told a news conference, adding that a Soviet delegation will visit Seoul next month to discuss economic and trade cooperation and that a high-level exchange of visits, possibly by heads of state, is being planned.

Shevardnadze called South Korea an important player in the quest for peace in Asia and said, "We believe that establishing diplomatic relations will aid the cause of stability in Asia and the Pacific region."

He added, however, that improved relations with South Korea would not adversely affect Soviet relations with any other state -- an indirect reference to North Korea.

The move is a potentially devastating blow to North Korea, which two days ago signed a communique with Japan calling for talks on normalizing ties after decades of enmity. The Pyongyang regime is one of the world's few remaining bastions of hard-line communism at a time when other Communist states are transforming themselves into nations with Western-style democracy and capitalism.

Since the division of the Korean peninsula into two antagonistic states at the end of World War II, the Soviet Union and China have been the North's principal allies and arms providers. In 1950, Soviet support emboldened North Korea to invade the South, prompting the United States to intervene in what became the three-year Korean War.

Now, Moscow is seeking help to bolster its crisis-ridden economy and has been eager for trade and investment from South Korea, which has blossomed into an economic powerhouse second only to Japan in northern Asia.

There was no immediate reaction from North Korea. But Kang Sok Ju, Pyongyang's first deputy foreign minister, told Post special correspondent Trevor Rowe in an interview here last week that the establishment of ties between Seoul and Moscow would have a negative impact on the fragile dialogue between the Koreas. Kang said that the normalization of ties would prompt Seoul to try to isolate the North even further and that Pyongyang would have to take appropriate measures to counter what it sees as an increased security threat.

For South Korea, ties with Moscow should boost its hopes of becoming a full member of the United Nations independently of North Korea. Pyongyang insists that the two Koreas must be unified, but it shows no signs of modifying its hostility and confrontational tactics toward South Korea's Western-oriented political and economic systems.

China also has shown interest in improving relations with Seoul, and Choi said today that he hopes Beijing will follow Moscow's example and open full diplomatic ties.

The further thawing of Soviet-Israeli ties was announced jointly by Shevardnadze and Levy following an hour-long meeting. They said that consulates general would be set up in Moscow and Tel Aviv, that the two ministers intend to meet regularly and that their ministries will establish regular contact.

The two countries began improving relations in 1987, when Moscow sent some diplomats to Israel to operate out of the Finnish Embassy. In 1988, Israel posted some low-level diplomats in the Dutch Embassy in Moscow.

However, steps toward full resumption of relations have been blocked by Soviet insistence that Israel must agree to an international conference on the Middle East and other measures to resolve the Palestinian question in ways acceptable to the Arab world.

One potential setback to the improvement of relations appears to have been resolved, this over the issue of direct airplane flights carrying emigrating Soviets Jews from Moscow to Israel.

After a period in which the Soviets appeared unwilling to move forward with the flights because of Arab sensibilities, a spokesman for Israeli Prime Minister Yitzhak Shamir announced in Jerusalem on Saturday that the direct flights would begin next month. Similar, unofficial reports came from Moscow.