SEOUL — The leaders of North and South Korea pledged today to seek a peace treaty to replace the Korean War’s 1953 cease-fire and expand projects to reduce tension across the world’s last Cold War frontier.

The pact came a day after a deal at China-hosted arms talks among North Korea, America, and other regional powers, in which Pyongyang promised to disable its main nuclear facilities and fully declare its nuclear programs by December 31.

The move would be the biggest step North Korea has taken to scale back its nuclear ambitions after decades of seeking to develop the world’s deadliest weapons. President Bush hailed it as a key for “peace and prosperity” in northeast Asia.

It was followed by the bilateral agreement capping three days of meetings in the North Korean capital, Pyongyang, between the North Korean leader, Kim Jong Il, and President Roh of South Korea. The two men “agreed to closely cooperate to end military hostility and ensure peace and easing of tension on the Korean peninsula,” according to a joint statement.

Substantive progress on any peace treaty would require the participation of America and China, which also fought in the conflict. South Korea never signed the 1953 armistice ending the war.

After signing the deal Messrs. Kim and Roh shook hands and posed for cameras. Mr. Roh then took Mr. Kim’s right hand in his left and raised both their arms in the air like champion prizefighters before the two shared a champagne toast.

“The South and North shared the view that they should end the current armistice regime and establish a permanent peace regime,” the pact said.

They also “agreed to cooperate to push for the issue of declaring the end” of the Korean War by staging a meeting of the “three or four heads of related states.”

Mr. Bush said last month that he is willing to formally end the Korean War, but insisted that it could only happen after Pyongyang’s total nuclear disarmament.

Pyongyang shut down its sole operating reactor at Yongbyon in July after America reversed its hard-line policy against the regime, the first concrete progress from years of talks that also include China, Japan, Russia, and South Korea.

The fast progress in the nuclear standoff has prompted Mr. Roh to push forward on peace efforts. But the Koreas accord today cited the nuclear issue in a single sentence, saying the North and South would make “joint efforts to ensure the smooth implementation” of previous accords from the six-nation arms talks “for the solution of the nuclear issue on the Korean peninsula.”

The two Koreas said they would hold “frequent” summits, although no timing for any future such encounters was given. Instead, the Koreas scheduled meetings between their defense and prime ministers in coming months to build on progress from this week’s summit.

The Koreas also pledged to boost economic ties, open regular cargo railway service along restored tracks crossing the Demilitarized Zone, and create a joint fishing zone on their disputed sea frontier.