But senior U.S. officials were reportedly told by Chinese counterparts in preparatory talks for the ministerial-level dialogue that Beijing would not tolerate any interference in the South China Sea, which was now part of China's core national sovereignty interests on a par with the rebel province of Taiwan, and restive Tibet and Xinjiang.

As if to underscore this increasingly assertive policy, China subsequently sent an impressive naval flotilla to exercise in waters around the Spratly Islands (disputed with Vietnam, the Philippines and Malaysia) in the southern sector of the South China Sea. It also enforced a fishing ban in the northern sector around the Paracel Islands (contested with Vietnam). This followed earlier pressure from China on U.S. energy company ExxonMobil to cease exploratory work off Vietnam in the South China Sea.

The United States is not geographically part of Asia. But it has territory in Hawaii in the central Pacific and Guam to the west, five Asia-Pacific alliances (with Japan, South Korea, the Philippines, Thailand and Australia), and extensive trade and investment ties with Asia.

Since Beijing's South China Sea claims may encompass as much as 80 percent of waters stretching from Singapore to the Taiwan Strait and affect free passage through one of the world's most important international sea lanes, the U.S. must have felt that the time had come for it to state publicly at a high level what American "core" interests were in the western Pacific.

Defense Secretary Robert Gates did so June 5 at the Asian Security Summit in Singapore. He stated that a peaceful and non-coerced resolution to the Taiwan issue was "an abiding national interest," adding that such an outcome was also vital for the overall security of Asia.

He also said that the South China Sea was an area of growing concern for the U.S. because it could affect regional stability. "We do not take sides on any competing sovereignty claims, but we oppose the use of force and actions that hinder freedom of navigation," Gates said.

Will China respect these U.S. interests, which are supported by Japan and many other Asian nations apprehensive at what China's rise might mean, especially without an effective counterbalance that only America can provide? China will not abandon its quest for national unity with Taiwan. But in the past two years, there has been a significant easing of tensions between the mainland and Taiwan, enabling productive negotiations between the two sides to proceed. This has taken place despite Beijing's objections to the sale of defensive U.S. weapons to Taiwan, and U.S. objections to the build-up of Chinese missiles aimed at Taiwan.

With Taiwan, Beijing probably feels that time and the balance of power and influence are on its side. So China can afford to be patient, avoiding the costs of conflict while eventually getting what it wants.

In the case of the South China Sea, the situation is more complicated and less in Beijing's favor. Since Chinese forces seized the Paracel Islands from Vietnam in 1974, China has consolidated its hold on the archipelago. But in the much larger Spratly chain to the south, China is in a relatively weak position in terms of the territory it actually holds.

Taiwan has the biggest island, Itu Aba. Vietnam, the Philippines and Malaysia hold all the atolls that are large enough for an airstrip. Many of them are now garrisoned with troops.

Vietnam occupies 29 of the Spratlys claimed by China, the Philippines eight, and Malaysia three. China holds about nine tiny bits of real estate, none of them with space for more than helicopter landing pads and cramped refueling docks for ships.

Although Chinese long-range military power is reaching the point where it could probably be used to evict some rival Spratly claimants by force, this would come at a high cost to China in damaged relations with the U.S. and many other Asia-Pacific states.

Somehow, ways must be found to prevent emotive nationalism and militarism from upsetting the uneasy status quo in the South China Sea. This calls for restraint from all claimants, but particularly from China and Vietnam. Both have been reinforcing their positions in the Spratlys in defiance of the spirit, if not the letter, of the voluntary Declaration on the Conduct of Parties in the South China Sea signed between ASEAN and China in 2002.

Perhaps the new forum for defense ministers from ASEAN, Australia, China, India, Japan, New Zealand, Russia, South Korea and the U.S. that will meet for the first time in Hanoi in October will help.

A real freeze on military reinforcement in the Spratlys is needed for a diplomatic thaw to take hold.