The second Asean-United States leaders' summit on Sept. 24 in New York may have conveyed the impression of an emerging alliance.

To be sure, after years of keeping a low profile on Southeast Asian problems, the United States is more engaged than ever. Secretary of State Hillary Clinton angered Beijing by taking a public position supporting Association of Southeast Asian Nations efforts to seek peaceful resolution of territorial disputes with China through multilateral diplomacy and for status of the South China Sea as a "maritime commons" rather than a territorial sea.

The image of Chinese expansion and US resistance has been reinforced by events to the immediate north in the East China Sea, after a Chinese fishing boat rammed a Japanese Coast Guard vessel off the disputed Senkaku-Diaoyu islands. China demanded release of the arrested captain, reparations and an apology from Tokyo.

Japan agreed to the release, but declared acquiescence to the latter two demands "unthinkable." Japan has been bolstered by Clinton's assertion that Japanese "administration" of the islands falls under the purview of the US-Japan Security Treaty and Defense Secretary Robert Gates' terse observation that the US "would fulfill our alliance obligations."

However, it would be a mistake to construe the New York summit as the beginning of a new Asian-American alliance against China. Despite anxieties about China's growing power, no Asean countries would be willing to put their money where their mouths are. Suddenly the US is seen as standing athwart Chinese strategic ambitions in Southeast Asia – with Asean governments apparently lining up in support of Washington against Beijing.

While much is valid in this characterization, it's crucial that US policymakers and strategists not over-read Clinton's comments in Hanoi, particularly when it comes to ASEAN support.

Beijing's strategic ambitions in Southeast Asia are real. From China's perspective, Southeast Asia is its southern doorstep – China has deep roots in the region derived from geography (a common border with Vietnam, Laos and Burma), ethnicity (large, economically powerful urban Chinese communities throughout the region) and history (the "tribute system" that expressed Southeast Asian deference to China over millennia).

In terms of strategic outlook, Chinese leadership evokes the classic realists of 19th century Europe – vitally concerned with prerogatives of sovereignty and the sanctity of borders, animated by calculations of power and influence. From the standpoint of the Chinese regime, Southeast Asia is properly understood as a natural and rightful Chinese sphere of influence, a region where China's interests are paramount. When these are properly acknowledged, China is prepared to adopt policies that benefit Southeast Asia as well as China – a dominion of Confucian harmony and benevolence. Since the mid-1990s China has emphasized the latter with a sophisticated diplomatic "charm offensive" designed to portray a good neighbor dedicated to the economic advancement of Chinese and Southeast Asians alike.

The South China Sea is central to this ambition, but in a special category. China presented an ox-tongue-shaped dotted line, calling it historic waters, effectively encompassing the entire South China Sea and cutting across the major sea lanes. Until recently Chinese officials have cloaked the Chinese claim in a shroud of ambiguity, epitomized by careful avoidance of the key word "sovereignty." Yet careful examination of Chinese statements and actions over the years left no room for doubt that China viewed the South China Sea as Chinese sovereign territory. Because China lacked the military capacity to enforce this assertion, it made strategic sense to obfuscate rather than clarify intentions. Deng Xiaoping often reminded his countrymen of a traditional Chinese aphorism: "Bide your time and conceal your capabilities until you are ready to act."

Clinton's statement at the Asian Regional Forum in Hanoi was delivered in the context of growing concern among Southeast Asian governments regarding China. For months Vietnam had complained publicly and through diplomatic channels about Chinese "bullying" of Vietnamese fishermen and international oil company crews that want to prospect off Vietnam's coast. Other Asean governments, while less overt, showed signs of disquiet over China's buildup of its armed forces, particularly those designed for offshore power projection. China's dam building on the upper Mekong, giving it control over that vital river system, has alarming implications for downstream states. The willingness of several Asean ministers to speak out in support of Clinton in Hanoi was testimony to US diplomatic preparatory spadework and growing unease.

There's no question that the US willingness to stake out a position in support of a maritime commons, not a territorial sea, and multilateral diplomacy, vice China's determination to deal with the Southeast Asian countries one at a time, was welcome in many regional capitals. It provided a vital, long overdue signal that ASEAN governments did not have to cope with China alone. In that sense Clinton's initiative has provided a dose of courage and self-confidence for ASEAN in its relationship with China.

That said, US policymakers must have a healthy respect for the limits of what Southeast Asian governments are able and willing to do. To employ an overused metaphor, at least some ASEAN members may be prepared to show up and hold America's coat if Washington duels Beijing. But don't expect them to get into the arena in any but carefully circumscribed ways – for a number of compelling reasons.

First, it's long been a truism that the Southeast Asian governments fear being forced to choose between China and America. No Southeast Asian country wants to make such a choice, but no less an authority than Singapore's widely respected ambassador to Washington, Chan Heng Chee, has observed that, if forced, the Southeast Asians would generally opt for China. There's a consensus in the region that the US-China relationship is vital to all concerned. When asked what kind of relationship best protects Southeast Asian interests, the answer is the proverbial Goldilocks principle – "not too hot and not too cold." A cooperative but not deeply collaborative relationship is just right.

Second, as previously noted, China's "influence and strategic reach into Southeast Asia is deep, powerful and growing. This is particularly evident in the economic sphere. As the global financial crisis weakened the credibility of the US and European economies, China emerged as the largest trading partner of Asean. Between 2009 and 2010, aggregate trade is up roughly 50 percent year on year. Not coincidentally, the China-Asean Free Trade Area entered into force at the beginning of 2010.

Third, despite significant investments in military modernization, no Southeast Asian country is prepared to confront China militarily. The only country that has done so in recent decades is Vietnam in response to China's 1979 invasion across its northern boundary. Vietnamese forces acquitted themselves well in that encounter, but Hanoi is under no illusion that such success could be replicated today. The only naval and air forces that can credibly face off against China in the South China Sea are American – and if it came to that, US commanders should expect little or no operational support from Asean, with the possible and limited exception of Vietnam.

Fourth, Asean is not the feckless cave of winds that some Westerners describe. But it's also not a unified, purposeful actor regarding the South China Sea. Several Asean governments, including Laos, Cambodia and Burma are highly responsive to Chinese interests and have no proverbial dog in the South China Sea fight. The best Washington can expect – and only if assiduously nurtured – is cautious diplomatic support along the lines of what was seen at the Asean forum. It's an important shift from the past that Washington should welcome, with realistic expectations.

Martin Ott is a public policy scholar with the Woodrow Wilson International Center for Scholars and adjunct professor and visiting research scholar with Johns Hopkins University. This is reprinted with the permission of the Yale Center for the Study of Globalization