The Soviet Union and South Korea agreed Saturday to broad new economic cooperation and a joint multibillion-dollar natural-gas development project in the Soviet Far East, said the state-run KBS-TV.

The Soviet Union also reaffirmed its position that if North Korea refuses to sign the nuclear-safeguard treaty it will suspend supplies of nuclear fuel, technology and other help to its longtime communist ally, KBS said.The agreements came during Saturday's summit talks between Soviet President Mikhail S. Gorbachev and South Korean President Roh Tae-woo.

Gorbachev is the first Soviet head of state ever to visit the divided Korean peninsula, and his trip has angered Moscow-backed communist North Korea, which views South Korea as an archenemy.

Gorbachev was scheduled to return to Moscow later Saturday following a formal announcement at the conclusion of the talks.

South Korea asked for Moscow's backing for Seoul's application for membership in the United Nations later this year. The Soviets reportedly said South Korea should make efforts to join the world body together with North Korea. If the north refuses, Moscow said it would be desirable for Seoul to join alone, KBS said.

This was interpreted to mean that Moscow would not veto Seoul's application, as it is empowered to do as one of the five U.N. Security Council members.

North Korea has been against separate U.N. seats for the Koreas and has proposed a single revolving joint seat, a proposal Seoul calls impractical.

Arriving late Friday at the tropical resort island Cheju, South Korea, on the last stop of an Asian tour, Gorbachev was greeted by thousands of cheering residents. But students who believe his visit could antagonize the communist north staged angry protests.

The project for the development of natural gas in Sakhalin Island would involve a consortium of Korean companies along with U.S. firms, said the highly placed sources.

An official for the powerful Hyundai Group, which was deeply involved in the plans, said the project was uncertain because it required a pipeline through communist North Korea.

In January, South Korea agreed to a $3 billion-dollar loan package and dozens of Korean firms are scrambling to form ties in the Soviet Union with the full encouragement of Seoul.