BEIJING — With President Hu Jintao at the helm, China has become a $5 trillion industrial colossus, a growing military force, and, it sometimes appears, a model of authoritarian decisiveness, navigating out of the global financial crisis and sealing its position as the world’s fastest rising power.

But as Mr. Hu prepares to visit Washington this week in an attempt to defuse tensions with the United States, Obama administration officials are grappling with what they describe as a more complex reality. China is far wealthier and more influential, but Mr. Hu also may be the weakest leader of the Communist era. He is less able to project authority than his predecessors were — and perhaps less able to keep relations between the world’s two largest economies from becoming more adversarial.

Mr. Hu’s strange encounter with Defense Secretary Robert M. Gates here last week — in which he was apparently unaware that his own air force had just test-flown China’s first stealth fighter — was only the latest case suggesting that he has been boxed in or circumvented by rival power centers.

American officials have spent years urging Mr. Hu to revalue China’s currency, rein in North Korea, ease up on dissidents and crack down on the copying of American technology, and they have felt at times that Mr. Hu agreed to address their concerns. But those problems have festered, and after first wondering if the Chinese leader was simply deflecting them or deceiving them, President Obama’s top advisers have concluded that Mr. Hu is often at the mercy of a diffuse ruling party in which generals, ministers and big corporate interests have more clout, and less deference, than they did in the days of Mao or Deng Xiaoping, who commanded basically unquestioned authority.

China’s military has sometimes pursued an independent approach to foreign policy. So have many of China’s biggest state-owned companies, sometimes to the United States’ detriment. The result is that relations between the world’s largest superpower and its fastest-rising one are at one of their lowest point in years, battered by confrontations that took Mr. Obama by surprise — and, on occasion, Mr. Hu as well.

Speaking on Wednesday to students at the Johns Hopkins School of Advanced International Studies, Treasury Secretary Timothy F. Geithner hinted that jockeying for power and an coming leadership transition have degraded China’s ability to set consistent policies.

“As China goes through this political transition over the next year or so,” he said, picking his words carefully, “in some ways, it’s having the effect of slowing the pace of reform because it’s inducing a bit of caution.”

Others are more stark. “There is a remarkable amount of chaos in the system, more than you ever saw dealing with the Chinese 20 years ago,” Brent Scowcroft, the former national security adviser and Mr. Gates’s mentor, said Saturday. “The military doesn’t participate in the system the way it once did. They are more autonomous — and so are a lot of others.”

Divided leadership has made it harder to resolve disputes with China, much less strike grand bargains like the reopening of relations between the two countries under Mao.

In past meetings, Mr. Hu and his prime minister have indicated that they would let China’s currency gradually rise. But the Commerce Ministry promptly labeled the move a “catastrophe” for the Chinese economy. Despite Mr. Hu’s repeated assurances that the Chinese market would continue to open up to foreigners, business leaders complain that regulators have made it more difficult for foreign energy, communications and banking concerns to compete with China’s state-backed favorites.

Not surprisingly, some of the biggest differences focus on how to deal with the United States and its power in the Pacific.

Mr. Hu has repeatedly asserted China’s disinclination to challenge American power; his designated foreign policy coordinator, State Councilor Dai Bingguo, recently wrote an article reaffirming Mr. Deng’s warning, made back when China’s modernization was beginning, that the country should bide its time before seeking a global role.

On Friday, the article was cited by Mr. Obama’s national security adviser, Thomas E. Donilon, who characterized it as “a definitive statement at this point of the leadership’s approach to foreign policy generally and the United States specifically.”

But even Mr. Donilon acknowledged debates “particularly in the blogosphere and in newspapers in China” that urge a far faster, more assertive rise, and that trumpet American decline. He said with some understatement that “following that debate is a very important thing to do.”

Adding to the uncertainty about Mr. Hu’s power is an expected leadership change in 2012. It is at once a choreographed transition to a new generation of leaders and a volatile minefield for all contenders, none of whom wish to be viewed as risk-takers, or as subservient to the United States.

Certainly, hopes that China and the United States, briefly dubbed the “G-2” when they started common action to counter the world economic crisis early in 2009, would suddenly find a coincidence of interests have turned out to be optimistic. Even when they agree, American officials report that turning talk into action is frustratingly slow.

By any measure, Mr. Hu is the most constrained Chinese leader in modern times. The notion that he could engineer a sweeping policy change the way that Mr. Deng threw open China’s economy three decades ago is unthinkable; more often he is a negotiator, brokering deals in a collective leadership where he has never seemed to fully consolidate power.

Part of his problem is systemic. As Mr. Gates discovered in his meeting last week, the absence of the equivalent of a National Security Council in China meant that the military could operate by its own rules. “The leadership forced the military to start talking to us again,” one senior administration official said, “but they couldn’t force it not to pull a stunt like the test flight while we were still in Beijing.”

Mr. Hu, of course, has the power, at least on paper, to reach across differing bureaucracies. Often, though, he cannot or will not. The debate over revaluing the renminbi, a constant thorn in the relationship with the United States, has not advanced much partly because of a fight between central bankers who want the currency to rise and ministers and party bosses who want to protect the vast industrial machine that depends on cheap exports for survival.

So far, the battle has made it impossible for China to act decisively — and it is struggling with inflation as a result. Mr. Obama’s aides now want to try a different tack: Rather than harp on currency, they are going to raise other economic issues and see if the pressure of rising inflation, and the fear that it could cause social unrest, will compel the Chinese to raise the value of their currency.

The rise of state-owned corporate behemoths, independent power centers in their own right, has also changed the politics in China and made it harder to address disputes with the United States and other big trading partners.

The administration’s latest report on Chinese trade practices, issued last month, says that the growing influence of these corporate giants raises significant questions about China’s support for “ongoing W.T.O. obligations, including core W.T.O. principles,” referring to the World Trade Organization.

China’s ban on exports of crucial rare earth minerals, cast by the government as a corporate decision made without state direction, is the most recent example of the tensions this drift toward state control has raised. But there are others: China Mobile, which dominates the nation’s vast wireless market, is pressing phone makers to adopt a Chinese standard for wireless communications that ignores the accepted global standard.

And entire swaths of the Chinese market remain broadly closed to outside competition, including banking, mobile communications, electronic payment processing and the media. Overhauling protected sectors of the economy is no longer a priority of the leadership.

Mr. Hu, of course, is hardly a helpless bystander to many of the decisions that rankle the United States. He is an architect of China’s growing repression of political dissidents and its recent efforts to expand its regional clout while the United States is on the economic ropes.

But Mr. Hu lacks the commanding authority of his predecessor, Jiang Zemin, or Mr. Deng.

China’s hawkish military undid years of careful diplomacy in the last two years as it flexed its muscles in the South China Sea, harassing American naval vessels and alarming neighboring countries.

No one questions China’s civilian control of the military. Mr. Hu and his presumed successor, Xi Jinping, sit atop the Central Military Commission, the body that oversees the military. But as with other parts of the bureaucracy, it is unclear how firm his grip is.

Abraham M. Denmark of the Center for a New American Security in Washington says there are “many, many examples” in which the military has blindsided civilian leaders with weapons displays or statements that appear to flout official policy. The issue, he said, is not whether the military is loyal to its civilian leaders but whether Mr. Hu and others can make it bow to the government’s broader foreign policy goals, like closer ties to the United States.