SEOUL, DEC. 13 -- South Korean President Roh Tae Woo today embarked on a trip to Moscow, carrying promises of economic cooperation to the beleaguered Soviet leadership.

The trip marks the first by a South Korean leader to the Soviet Union. The two countries had been enemies since the Korean War, and they established diplomatic relations only last September when Roh met with Soviet President Mikhail Gorbachev in San Francisco.

Beyond its significance as a milestone in the thawing of the Cold War in Asia, the voyage underscores the enormous internal changes that have swept both nations in recent years.

Roh's small country is leaping forward economically. Gorbachev's giant nation has fallen on hard times. Roh's plans to offer trade and investment opportunities -- probably along with economic aid -- to the Soviets signify a new stage in South Korea's emergence as a power. The event has stirred considerable pride here. In a typical newspaper commentary, the English-language Korea Herald declared that Roh's trip "represents the rising stature of Korea in the world community."

Roh's departure came as the North and South Korean prime ministers wound up the third in their historic series of meetings.

The talks here between the Communist North's Yon Hyong Muk and the capitalist South's Kang Young Hoon produced little more than an agreement to meet again in February in North Korea's capital, Pyongyang. As expected, vast differences remain over how to reunify the Korean Peninsula, divided since 1945.

But even as the two sides -- still technically at war -- leveled criticism at each other, they stressed that the talks were valuable in slowly developing trust and goodwill. "Although we didn't produce a visible result," a South Korean government spokesman said, "invisible gains were accumulated that may sooner or later narrow the gap."

Roh's overtures to Moscow are aimed partly at isolating North Korea and weakening its threat to Seoul. The Soviets have been North Korea's most important ally, and Moscow's blooming relationship with the South has come as a severe setback to Pyongyang. With its formidable financial strength and business acumen, South Korea has become an attractive partner for the Soviets.

South Korean newspapers have reported that Roh will offer $500 million in hard-currency loans to Moscow. Officials here say the precise amount and shape of the economic assistance remain undecided.

Beyond outright assistance, Roh will offer the prospect of billions of dollars in investments by South Korean companies, a number of which have dispatched top executives to Moscow during Roh's trip. The companies are eagerly seeking to establish joint ventures in the Soviet Union to produce goods.