Experts said the United States, China as well as the rest of Asia - whether it's South Korea and Japan in the northeast or Indonesia, Singapore, Vietnam and Laos in the southeast - all seek and stand to gain from cooperation.

"I don't see this as a contest. It's not a zero-sum game," said Joe Lieberthal, a Brookings Institution analyst in Washington who served on former president Bill Clinton's National Security Council.

Nonetheless Lieberthal told reporter that Washington's return to its traditional robust role in the Pacific could irk China to the point that it harms bilateral relations, a situation where both nations would lose.

"The concern obviously is whether this is having a serious negative impact on our ties with China, or whether these are kind of bumps in the road," Lieberthal said.

He suspects some in Beijing's leadership believe that the Obama administration will boost the confidence of China's smaller neighbors to the point it becomes harder for the Asian power to have its way in the region.

The U.S.-China balance, experts said, has shifted since President Barack Obama took office last year promising to "re-engage" with a region which predecessor George W. Bush's administration had neglected as it focused on the war on terror.

The Asia-Pacific has since seen a flurry of visits by not only Secretary of State Hillary Clinton, Defense Secretary Robert Gates and other cabinet members but also senior officials from various government agencies.

Obama, who calls himself the first "Pacific" U.S. president as he was born and raised in Hawaii, has also visited the region although he has twice postponed plans to travel to Indonesia, where he spent part of his childhood.

"We haven't seen this kind of diplomatic attention by the United States to the region at senior levels, where it counts, for a long time," said Douglas Paal, who has served in previous U.S. administrations.

"It reminds me of what the Chinese did after 1998, when they sort of woke up and thought Southeast Asia was important," said Paal, now a leading analyst at the Carnegie Endowment for International Peace.

"More recently China's game has slipped," he said.

Not only is China no longer sending its "cream of the crop" of diplomats to Southeast Asia, he said, it has worried neighbors like Vietnam with unilateral steps on disputed islands in the South China Sea.

The United States has now stepped into the tangle.

On a visit to Hanoi last week for the ASEAN (Association of South East Asian Nations) Regional Forum, a 27-member grouping, Clinton said Washington had an interest in guaranteeing open navigation and free trade in the South China Sea.

In remarks apparently coordinated with her ASEAN partners, the chief U.S. diplomat also said Washington would be willing to facilitate multilateral talks on the islands.

Chinese Foreign Minister Yang Jiechi later warned the United States not to internationalize the issue, saying direct bilateral talks were the path to take.

What Clinton did was burnish U.S. credentials as a counterweight to China.

The United States is "getting back into the game of balancing China in the eyes of many of the states in the region who feel they can't stand up to China alone and they need someone to pull them together collectively," Paal said.

China, he said, has also bolstered Washington's own alliance with South Korea and Japan by failing to take a stronger stand on the sinking in March of a South Korean warship by what Seoul says was a North Korean torpedo.

Bonnie Glaser, a China expert with the Center for Strategic and International Studies who has been a consultant for the State and Defense Departments, said Asian nations have cooled toward China and warmed to the United States.

"Most of the states in the region really welcomed China's rise," she said, citing new trade and investment opportunities there.

"But increasingly countries think that China has been given a little bit too much running room, that there does need to be more balance and that the best power to do that is the United States," Glaser told reporter.

"I think the Chinese really got out in front of us in the last decade and the U.S. is really now sort of catching up," she added.