"The US needs to do more than be engaged. It needs to give the region the sense that the dynamism is on the US side. Right now, it's on the Chinese side," says Michael Montesano, a visiting fellow at the Institute of Southeast Asian Studies in Singapore.
The US remains the preeminent military power in Asia and the guarantor of open sea lanes that carry a significant share of trade in oil, food, and manufactured goods. Few expect that power to wane in the short term, despite the expansion of China's naval capacity.
On Wednesday, Clinton signed a Treaty of Amity and Cooperation with the Association of Southeast Asian Nations (ASEAN), which is hosting the summit. Its secretary-general, Surin Pitsuwan, said it was "a shift in strategy on the part of the new US administration toward ASEAN."
In reality, the treaty is largely symbolic, say analysts. China signed it in 2003, as have other major powers, but it's unlikely to bear much weight on potential flash points in the region, including sea boundaries between China and Vietnam and disputed islands such as the Spratleys.