Hours after winning the South Korean presidency, Roh Moo-hyun underscored the importance of his country's ties with the United States, but said the relationship between the two should undergo adjustments.

South Korean President-elect Roh Moo-hyun is calling for changes in South Korea's decades-old alliance with the United States, but he says they should take place gradually.

He said he will continue to cooperate with Washington and its allies regarding North Korea's nuclear weapons development.

Mr. Roh says South Korea will play an active role in solving the issue of North Korea's nuclear program. He says it will closely cooperate with the United States and Japan on the matter.

North Korea told the United States it maintains a secret weapons development program, and has also threatened to restart aging facilities that could produce fuel for nuclear weapons.

Mr. Roh, a former labor lawyer and human rights activist, won Thursday's election in a close race with opposition leader Lee Hoi-chang. While campaigning, Mr. Roh pledged to seek more independence from Washington, which has 37,000 troops stationed in the country. At a news conference, the president-elect said the friendship between South Korea and the United States must "mature" and advance in the 21st century. It recently came under pressure after two U.S. soldiers accidentally hit and killed two Korean girls with their armored vehicle.

The soldiers were acquitted in a U.S. military trial last month, and tens of thousands of South Koreans took to the streets to protest the acquittals.

Washington's current Status of Forces Agreement with Seoul stipulates that cases like this be tried in U.S. military courts. Mr. Roh has said he would like to change that agreement to give South Korea more control over such cases.

Officials from the United States, South Korea and their allies have been discussing how to put diplomatic pressure on North Korea to halt its weapons program.

The Bush administration has ruled out talks with the North unless it does so, but Mr. Roh has pledged to continue the engagement policy of outgoing President Kim Dae-jung, which calls for aid, business deals and cultural exchanges to help bring Pyongyang out of its shell.

Yonsei University Professor Lee Chung-min predicts that South Korea and the United States face a lengthy and awkward transition period.

"There will be tensions between Seoul and Washington on how to deal with one of the most important proliferators in the world community today," he said. "Having said that, the Bush administration has no choice [but] to work with Mr. Roh, but there will be a lot of tension, both on surface and below."

The Bush administration moved quickly Thursday to congratulate Mr. Roh on his electoral victory and pledged cooperation with the incoming administration.