The United States plays an "indispensable" role in Asia despite the rise of China and India and should be part of any new regional group, Singapore Prime Minister Lee Hsien Loong said Tuesday.

Speaking ahead of the Asia-Pacific Economic Cooperation (APEC) summit, Lee expressed hope Washington will deepen engagement in the region despite pressing domestic issues and worries over Iraq, the Middle East and Afghanistan.

"We believe America plays an indispensable role in Asia in many fields - economic, political, strategic, security," he said at a news conference.

"We've been talking about a multipolar world, but de facto the US is the most powerful nation in the world and will be so for some time to come."

US President Barack Obama, Lee and 19 other world leaders will gather in Singapore from November 13-15 for the annual APEC summit and dialogue with global corporate chiefs.

Lee's comments came amid a debate in diplomatic circles about the US role in various proposed free-trade zones and economic communities in the region.

At an Asian summit last month in Thailand, Japan spoke of its vision for an East Asian Community and Australian Prime Minister Kevin Rudd outlined his idea for an Asia Pacific Community.

Japanese premier Yukio Hatoyama, at the Thailand summit, was unclear on the extent of proposed US involvement but Rudd's vision includes Washington.

While China has not made public any proposal so far, diplomats say Beijing favours a free-trade zone comprising the 10 Association of Southeast Asian Nations (ASEAN) members plus China, Japan and South Korea.

Lee said Washington's role in Asia comes not only from its economic and military might, but also from its post-World War II contribution to a stable security environment that allowed Asia-Pacific nations to prosper.

"I think all (APEC) participants acknowledge that it is important for Asia, while it is working on regional cooperation, to also maintain an open and an inclusive framework of cooperation which does not exclude the US and does not exclude Europe," he said.