But the limits of Manila’s influence were revealed shortly after Mr. Aquino’s visit, when the mainland Chinese authorities executed three Filipinos accused of drug trafficking despite Mr. Aquino’s clemency pleas. The executions, and an increase in skirmishes between fishermen and naval vessels from both countries, have fueled Philippine determination to stand up to Beijing.

Walden Bello, a congressman who made a symbolic touchdown on one of the contested islands last summer, said the Philippines was grappling with the realization that China’s economic prowess would probably eclipse that of United States.

“Everybody has been affected by the sense that American power is on the wane and that China’s is on the rise,” he said. “But the fact that China would make such a brash and astounding claim to the entire South China Sea is disconcerting. I think there’s a feeling that we can’t allow our economic dependence on China let them trample all over us.”

China does not claim that the entire South China Sea is under its sovereignty. But it does make disputed claims to island territories in the sea that would, if recognized, give it sway over developing resources in large parts of the sea, which are among the world’s busiest shipping lanes.

The sea has substantial oil and gas reserves that, if fully developed, could someday rival those of Kuwait. Also at stake are rich fishing grounds that by some estimates supply about a tenth of the world’s commercial seafood.

In injecting itself into the dispute — beginning last year when Mrs. Clinton declared the issue a matter of “national interest” — the United States has emphasized the area’s crucial role as a conduit for maritime trade.

Despite its vulnerable economy and a weak military that relies on warships from World War II, the Philippines has not shied away from confrontation. In a gesture of patriotic bravado, government officials and the news media have taken to calling the region the West Philippine Sea, and Mr. Aquino has been vocally asserting claims to the islands, some of which are less than 50 miles off the coast of Palawan but more than 500 miles from China’s southernmost province.