North Korea is building what appears to be an underground missile-launching base within a dozen miles of the Chinese border, a South Korean presidential spokesman said today.

"Something is being built in that location, and the South Korean and American military are very concerned about it," Chung Eun Sung, press secretary to President Kim Dae Jung, said in an interview.

Chung said that based on intelligence reports, South Korea has a "well-grounded assumption" that the site under construction in the mountainous area of Yeongjeo-dong, is a launching platform for North Korea's Taepodong I ballistic missiles and its more advanced Taepodong II model.

Reports of the potential missile base come amid concerns that North Korea is preparing to test-launch, from a different site, a Taepodong II missile with sufficient range to reach Alaska or Hawaii. Just five days ago, President Clinton and President Kim met in Washington and warned North Korea that any further missile tests on its part would pose "a serious obstacle to peace."

Today, North Korea reiterated its stance that testing ballistic missiles is a "sovereign right" and criticized the United States for suggesting a launch would threaten bilateral agreements with Pyongyang.

"We have already repeatedly declared that such things as missile development, production and test-launch belong to our sovereignty, and no one has the right to take issue with the rights of a sovereign state," said the Korean Central News Agency, monitored in Tokyo.

U.S. military officials in Seoul and a spokesman for the U.S. Embassy in Seoul declined to comment today on reports of the suspected missile site. In Washington, Clinton administration officials declined to comment, citing intelligence concerns.

Word of the Yeongjeo-dong site has circulated for months in intelligence circles; Chung issued his confirmation when asked about a story on the site in a leading South Korean newspaper today.

The story in the Chosun Ilbo stressed that the site would be difficult for South Korea or the United States to attack because it is located so close to Chinese territory and because it is built into a mountainside facing China.

The new emphasis on the site's proximity to China suggests that Washington, Seoul and Tokyo are hoping Beijing will take a tougher stance on North Korea's fledgling missile program. Before NATO jets mistakenly bombed the Chinese Embassy in Belgrade during the Yugoslav war, Beijing was believed to be strongly supportive of U.S. and South Korean efforts to expand peaceful contacts with North Korea. Since then, Beijing appears to have been rethinking its strategic interests and has been generally less cooperative with the United States.

Japanese Prime Minister Keizo Obuchi is scheduled to travel to China Thursday for a long-planned meeting with President Jiang Zemin. North Korea's missile program will be high on Obuchi's agenda. It is unclear what stance Jiang will take, but press reports from Beijing this week said Jiang has no intention of discussing the issue.

Any new North Korean missile base could complicate delicate U.S. and South Korean diplomatic efforts to approach the reclusive Pyongyang regime. North Korea, one of the world's largest exporters of tactical missiles, raised alarm across Asia last August when it test-fired a Taepodong I over Japanese territory into the Pacific Ocean. As reports spread that it may soon test-fire another missile, Pyongyang's defiance has deeply concerned officials in Seoul, Washington and Tokyo.

Clinton is facing severe criticism in Congress over his policies toward North Korea, which has moved to increase missile sales to pariah states and become involved in drug smuggling and counterfeiting to combat its chronic food shortages and other economic problems.

A lengthy review of U.S. North Korea policy by former defense secretary William J. Perry is nearly complete and is believed to include a comprehensive package of enticements for Pyongyang to give up its missile programs and nuclear weapons ambitions.

Today's Chosun Ilbo story said that the suspected missile base reportedly has 10 launch pads and is about 70 percent complete. The paper said North Korea has 10 missile bases and is building three underground ones, including the Yeongjeo-dong site, near the middle of North Korea's border with China.