President Bush reassured Pacific Rim leaders Thursday that the United States stands squarely behind moves to liberalize trade with the region, and he promised continued support for efforts to battle terrorism and disease and to pressure North Korea to abandon its nuclear weapons program.

In a speech at the National University of Singapore on the eve of a summit in Hanoi of the Asia-Pacific Economic Cooperation forum, Bush voiced tentative support for a free-trade agreement covering all 21 APEC nations, saying the idea deserves "serious consideration."

In addition, the president again warned North Korea that the United States would consider it a "grave threat" and would hold North Korea responsible if it transfers nuclear bomb technology to another country or to a terrorist organization. He said North Korea should take "concrete steps" to end its nuclear program, and he called on other Asian countries to send the same message to the reclusive communist regime in Pyongyang.

North Korea agreed to resume talks with five other nations on ending its nuclear weapons program last month, just weeks after conducting its first nuclear weapons test. Diplomats hope talks among North and South Korea, China, Japan, Russia and the United States will take place by the end of the year, but no date has been fixed.

In comments to reporters at the APEC meeting in Vietnam, Secretary of State Condoleezza Rice said there was deep skepticism among the group's members that North Korea actually intended to abandon its nuclear weapons. Bush is scheduled to join Rice in Hanoi after leaving Singapore Friday morning.

Asked if she would favor delaying talks until she was certain that North Korea would take steps to show its commitment, Rice said: "I don't think it makes sense for us to have talks unless we think that it's going to be fruitful. It certainly doesn't make sense just to go back to talk."

In his speech, Bush also called on North Korean to take demonstrable action to show it is willing to end its weapons program. "Pyongyang must show it's serious -- show it is serious by taking concrete steps to implement its agreement to give up its nuclear weapons and weapons program," he said.

Bush added that if North Korea gives up its nuclear weapons, the United States and other nations involved in the six-party talks would provide economic help, security assurances and other benefits to North Korea.

Bush's visit to Southeast Asia comes on the heels of U.S. midterm elections in which Democrats won majorities in both houses of Congress, an outcome widely seen as a repudiation of the president's leadership.

Many nations in Southeast Asia, which have a generally warm view of Bush, see the United States as a pillar of stability in a region where Communist-run China is the dominant force, some analysts say.

With Bush weakened politically, the analysts say, some leaders in this economically booming region of the world would be dubious of his power to deliver on his trade liberalization and other promises.

Bush suffered a setback earlier this week when the House of Representatives failed to approve a measure to grant permanent normal trade relations to Vietnam. Bush had hoped that Congress would approve the measure before his trip to Hanoi, but House leaders now say they will not try to pass the bill again until sometime next month.

Passage of the bill is needed for firms in the United States to take advantage of the low tariffs Vietnam will enact as a result of joining the World Trade Organization. The failure to pass the bill was viewed as a disappointment both by the Bush administration and the Vietnamese government.

In his address previewing issues he plans to emphasize during his week-long trip, Bush said the United States is serious about helping the region meet the challenges that could undermine its recent record of explosive economic growth. He cited efforts to help develop alternative energy sources, fight pandemics such as AIDS and avian flu and combat terrorism.

Pointing out that the United States conducts more trade across the Pacific Ocean than across the Atlantic, Bush said he wants the United States to remain deeply involved in the region.

"In this new century, America will remain engaged in Asia, because our interests depend on the expansion of freedom and opportunity in this region," he said.

Before his speech, the president met with Singapore's prime minister, Lee Hsien Loong. He also visited the Asian Civilizations Museum. Accompanied by his wife, Laura, he listened to a performance of Asian fusion music.

At one point, Bush briefly played the saron -- an Asian xylophone -- managing to tap out a passable rhythm with a rubber mallet.

The president is scheduled to spend three nights in Vietnam, then stop in Indonesia and Honolulu before returning to Washington on Tuesday.