IRVINE, CALIFORNIA – China’s government has been using unusually strong language of late to assert its sovereignty over disputed stretches of international waters near to its shores. This has led to a ratcheting up of tensions, in particular between China and the United States, with Secretary of State Hillary Clinton stressing that the Obama administration is now ready to step in and help ensure the fair adjudication of disputes relating to the South China Sea. Chinese spokesmen denounced this as a throwback to the days when America thought it could, and should, try to “contain” the People’s Republic.

One way to interpret China’s elevated rhetoric – and its tough response to joint US-South Korean military maneuvers – is as another indication that Chinese leaders have grown supremely self-confident and are eager to throw their weight around. The reality, though, is more complex. A closer look reveals that President Hu Jintao’s words and deeds are often shaped by a mixture of insecurity and cockiness, and that Chinese officials alternate between playing up and playing down the country’s rise.

Of course, there are moments when China’s leaders do seem like people who know that they are succeeding and want others to acknowledge it. Even before the current diplomatic controversies, China’s leaders were gleefully drawing attention to how much more effective their stimulus package had been than Obama’s in countering the negative effects of the financial crisis.

And yet, when news broke last month that China had officially replaced Japan as the world’s second-largest economy, instead of crowing about surpassing a longtime rival and having the top spot, held by the US, in its sights, the government issued statements emphasizing that theirs remains a “poor, developing” country.

The self-confident side of the leadership’s split personality is often what worries China’s neighbors and the US alike. Still, it is important to remember that there’s a positive aspect to the Party’s self-confidence. As political scientist Kevin O’Brien has argued, China’s increased readiness to compromise with some domestic protesters, rather than treat all forms of collective action as subversive, can be seen as reflecting a growing sense of security.

Conversely, some of China’s most disturbing moves can be chalked up to exaggerated feelings of insecurity. Consider the harsh treatment of the gadfly critic Liu Xiaobao, sentenced to 11 years in prison on trumped-up charges of “subversion” for launching an Internet petition drive championing civil liberties. Would a truly self-confident ruling elite have been so skittish about his activism?

The confident side of the Chinese leadership’s split personality is easy to understand. From the late 1980’s until 2000, many observers presented the Party as being on its last legs, certain to succumb to the “Leninist extinction” that began with communism’s collapse in Europe. But the Party remains in charge today. Airport bookstores that once displayed Gordon G. Chang’s ‘The Coming Collapse of China’ now offer Martin Jacques’ When China Rules the World.

Why, then, do China’s rulers continue to backslide into doubt and fear, and why do they seek to avoid having China labeled a superpower?

For starters, downplaying China’s rise has practical benefits. It helps to be seen as a “poor, developing” country, not as an economic giant, because “developed” nations are expected to do more to combat major global challenges, like climate change.

At the same time, China really is still a “poor” country in terms of per capita income. And parts of the country are more similar to sections of troubled “developing” countries than to China’s showplace cities.

The Party is in a vulnerable position – and knows it. That is no excuse for paranoia and repression, but just because the Party has outlasted predictions of its demise does not mean that it has no Achilles heel. Most notably, the anger over corruption and nepotism that fueled the Tiananmen protests has never gone away.

China’s leaders thus continue to depend on a form of nationalism structured around tales of victimhood. They now base their legitimacy on the notion that the Party, which rose to power as the nation fought foreign domination, is uniquely qualified to keep China from being bullied in a hostile international arena, and that only they can provide the stable environment needed for growth.

The Chinese leadership’s split personality explains a curious phenomenon that former US State Department adviser Susan Shirk noted in her book China: Fragile Superpower. When she mentioned the book’s title to American friends, they wondered why she used the modifier “fragile,” whereas Chinese friends said calling their country a “superpower” was premature.

Shirk’s title still captures a significant phenomenon that bedevils diplomatic affairs. Outsiders are increasingly convinced that China is a superpower, and that it needs to show that it can be a responsible one. But China’s rulers only sometimes embrace the designation – and the Party still sometimes behaves as if it had only a tenuous hold on power.

– Jeffrey Wasserstrom is Professor of History at the University of California, Irvine, and Editor of The Journal of Asian Studies. His most recent book is China in the 21st Century: What Everyone Needs to Know