In November 2011, President Obama stood before the Australian Parliament and issued a veiled challenge to China's ambitions in Asia: "As a Pacific nation, the United States will play a larger and long-term role in shaping this region and its future." A year later, the details of his pledge — along with a nascent American military buildup in the Pacific — are emerging.

China, which has spent the past year asserting territorial claims to disputed islands that would give it vast control over oil and gas rights in the East and South China Seas, remains suspicious about American intentions.

In an amphibious warfare drill on Guam in September, which did not go unnoticed in Beijing, Japan's Self-Defense Forces and American Marines "retook" a remote island from an unnamed enemy.

The Japanese government canceled a joint amphibious landing on a remote island near Okinawa that was to have been part of an enormous annual exercise of the American and Japanese militaries last week. The cancellation was an effort not to provoke China, which is locked in a dispute with Japan over the control of uninhabited islands near Okinawa in the East China Sea.

Pentagon officials nonetheless say that the Marines are an important symbol of America's long-term commitment to the Pacific. Under an agreement with Australia, the Pentagon anticipates that the company of 250 Marines that arrived in Darwin in April for a six-month rotation will grow to a battalion of 1,000 Marines in 2013. By 2016, assuming more housing is built, the Marines are expected to number 2,500.

They also say that if Congress does not agree to a fiscal deal this fall, the Pentagon will not be able to pay for much of the Asia strategy.