PRESIDENT Roh Tae-woo declared yesterday that South Korea was free of nuclear weapons and urged North Korea to join in making the peninsula a nuclear-free zone."As I speak, there do not exist any nuclear weapons whatsoever anywhere in the Republic of Korea," Mr. Roh said in a televised speech. Roh's declaration confirmed that the United States had removed its nuclear weapons from the South. It gave his administration strong leverage in its campaign to force Pyongyang to renounce its suspected nuclear arms development. The North, which maintains its nuclear plants are for peaceful purposes, says it would allow outside inspections if Washington began withdrawing its nuclear arms from the South. Seoul and its allies believe North Korea's nuclear program, centered at Yongbyon, north of Pyongyang, aims to build a bomb. US officials have called it the gravest threat to regional security. Roh said there was "no reason or excuse" for North Korea to develop nuclear arms or refuse inspections now that the South was nuclear-free. "North Korea must forthwith conclude and ratify a nuclear safeguards agreement with the International Atomic Energy Agency, shut down all nuclear processing and enrichment facilities, and submit unconditionally to international inspection," Roh said. The presidential speech did not directly mention the issue of US nuclear weapons. But a senior government official said the statement meant such weapons had already been removed. About 39,000 US troops are stationed in South Korea, still technically at war with the North, one of the world's last Stalinist states. Washington neither confirms nor denies the presence of its nuclear arms overseas. In September, President Bush said the United States would eliminate its tactical nuclear weapons deployed worldwide. US newspaper reports have said this included about 100 nuclear weapons stored at Kunsan Air Base south of Seoul. The two Koreas, which fought from 1950 to 1953, last week signed a nonaggression pact.