MANILA — President Obama called on China on Wednesday to halt its construction on reclaimed islands in the South China Sea, raising the contentious issue at the start of a two-day economic summit meeting at which he and other Pacific Rim leaders also discussed trade and climate change.

Speaking to reporters after a meeting with President Benigno S. Aquino III of the Philippines, Mr. Obama directly addressed the disputed Chinese claims to islands in the critical waterway. He urged the Chinese to stop military activities there and endorsed a process of arbitration to settle differences between Beijing and its Southeast Asian neighbors.

“We agree on the need for bold steps to lower tensions, including pledging to halt further reclamation, new construction and militarization of disputed areas in the South China Sea,” Mr. Obama said.

The United States takes no position on the territorial claims of various Asian governments in the region, but Mr. Obama has aggressively sought to defend the right of free navigation in the South China Sea, a vital route for commerce and trade. On Tuesday, he announced $250 million in military contributions to several Asian nations to support their efforts to stand up to China.