SEOUL, OCT. 18 -- A slow thaw between the rival Koreas apparently speeded up today when North Korean President Kim Il Sung conditionally agreed to meet with South Korean President Roh Tae Woo.

Kim conveyed his position during a cordial meeting with South Korean Prime Minister Kang Young Hoon, the highest official from capitalist Seoul to visit Communist Pyongyang in more than four decades. But Kim strongly indicated that talks between Kang and his North Korean counterpart must first achieve concrete results.

"If the prime ministers' talks proceed well, I can meet President Roh Tae Woo and the summit talks will proceed in a good way," Kim said, according to transcripts relayed to Seoul by reporters in Pyongyang. This important caveat could be an attempt to delay a summit, observers said.

Kang arrived in Pyongyang on Tuesday for the second round of talks with North Korean Prime Minister Yon Hyong Muk, who came to Seoul a month ago. The prime ministers ended their talks this morning without any accords, but they agreed to meet again in Seoul Dec. 11-14.

Sessions between the prime ministers, who are considered to be figureheads under powerful presidents, were spiced with discord. But officials on both sides expressed satisfaction, and a joint statement predicted "a substantial achievement" in December.

The North Korean prime minister has proposed a nonaggression pact, but the South Korean prime minister has countered with a declaration on political cooperation. North Korea has focused on arms control as the key route to reduced tensions, but South Korea has contended that such measures as mutual recognition and economic exchanges should precede military adjustments.

The future talks between ex-general Kang and technocrat Yon seem likely to focus on merging their differing proposals into a joint document that their presidents could sign at a summit.

The two Koreas are still technically at war. They agreed only to a truce, not a peace treaty, to end the 1950-53 Korean War. Their sealed border, surrounded by 1.5 million troops, is one of the Cold War's last outposts. Past efforts to relax tensions have sputtered once the time came to move past rhetoric and make compromises.

Kang's meeting with President Kim at his official residence began with a handshake and smiles for photographers. They met for about 20 minutes in private and were then joined by more than a dozen senior officials.

South Korean officials in Seoul expressed satisfaction with the meeting, noting that "Great Leader" Kim referred to President Roh Tae Woo by his proper official title. In the past, Kim and other senior North Koreans have avoided such diplomatic formalities, saying they view the South Korean government as an illegitimate "puppet state" controlled by Washington.

But mixed signals continue to be sent out by North Korea as it wrestles for a strategy to support its ailing economy while its key allies reduce their support in favor of political and trade ties with thriving South Korea. Last month, the Soviet Union agreed to establish diplomatic relations with Seoul, which also has booming economic relations with China.

North Korea, in a major turnabout, has asked longtime enemy Japan to start negotiations on establishing diplomatic relations. It also wants to improve its limited contacts with the United States.