North Korea declared today that its sea border with South Korea is invalid and asserted that its territorial waters extend 35 to 40 miles south of a line of separation set in 1953 after the Korean War.

North Korea's latest provocative claim, an example of the conflicting signals emanating from Pyongyang in recent years, came as the isolated Communist state appeared to have put on temporary hold its plans to test-fire a long-range ballistic missile--at least until its representatives meet with U.S. officials in Berlin beginning Tuesday.

South Korea promptly dismissed the border claim as "old, worn-out tactics," but the potential for conflict over the issue was apparent in a June 15 naval clash between North and South Korean ships in those same disputed waters.

A North Korean patrol boat was sunk in that action, one of the most violent naval confrontations since the Korean War, and various reports have estimated that between 30 and 80 North Korean seamen were killed.

In asserting the border claim, a broadcast by Pyongyang's official news service denounced the "brigandish" postwar drawing of the "Northern Limit Line," which has served as the the Yellow Sea boundary between the rival Koreas for nearly a half-century. "Our self-defense right" will be exercised by various means and methods," the broadcast said, a warning attributed to the North Korean army.

The new border claim followed an apparently fruitless meeting Wednesday between North Korean and U.N. officials in the truce village of Panmunjom--the sixth session called to try to resolve tensions heightened by the Yellow Sea clash. The North Korean broadcast declared: "We will no longer waste time sitting face-to-face with the U.S. forces side."

North Korea unnerved its Asian neighbors a year ago by firing a missile that overflew Japan. The United States, Japan and South Korea have warned North Korea not to test a new, longer-range version of that missile, and those cautions may have prompted the Pyongyang government to agree to the Berlin negotiations.

Japanese Prime Minister Keizo Obuchi, meeting today in Tokyo with his South Korean counterpart, Kim Jong Pil, applauded North Korea's "somewhat flexible remarks" on the testing of the new missile. The two officials said North Korea can expect improved relations if it forgoes the test, and less assistance if it launches a missile.

North Korea has frequently demonstrated a desire to improve relations with the United States on the one hand, while continuing to issue threats and bombast on the other.

Its claim today to a large new swath of sea territory could be mere rhetoric, but if it tries to enforce the claim by sending ships to the area, the likely confrontation with South Korea would create a flash point.

"Our will to defend the area is firm and resolute," South Korean Defense Ministry spokesman Yoon Il Young told reporters in Seoul.

Also in Seoul, Russian Defense Minister Igor Sergeyev and his South Korean counterpart, Cho Seong Tae, agreed to work closely to try to stop North Korea from launching the new missile, the Associated Press reported.

There was no explanation on how the two countries would cooperate, but Sergeyev said recently that Moscow is trying to persuade North Korea through political and diplomatic channels to forgo the test.

The Korean War did not end with a formal peace treaty, but with an armistice agreement signed in 1953 that did not demarcate a sea border between the rival Koreas.

The U.S.-led U.N. force that monitors the armistice agreement set the Northern Limit Line in the Yellow Sea to try to avert clashes between the North and South, but North Korea has consistently demanded a "legitimate" border farther south.