U.S. Vice President Joe Biden will try to strike a delicate balance of calming military tensions with China while supporting ally Japan against Beijing on a trip to Asia this week that is being overshadowed by a territorial dispute in the East China Sea.
Aiming to counter criticism that the United States is neglecting Asia because it is distracted by domestic politics and the Middle East, the White House has long been planning a visit by Biden to Japan, China and South Korea.
(Read more: China scrambles jets to new defense zone)
Those countries are at the heart of a quarrel over two tiny islands claimed by both Tokyo and Beijing that descended into military brinkmanship after China in late November declared an "air defense identification zone" that includes the islands.
In Tokyo on Tuesday, Biden will likely assure Japan that a military alliance with the United States dating back to the 1950s remains valid as the government of Prime Minister Shinzo Abe wrangles with China over the islands.
Yet he will also try to calm tensions between the United States and China over the same territorial dispute when he goes to Beijing later in the week.
"It's especially important ... that we continue to amplify our messages that we are and always will be there for our allies, and that there is a way for two major powers in the U.S. and China to build a different kind of relationship for the 21st century," a senior Obama administration official said.
Although Washington takes no position on the sovereignty of the uninhabited islands, it recognizes Tokyo's administrative control and says the U.S.-Japan security pact applies to them, in a stance that counters China's attempts to challenge U.S. military dominance in the region.
"I think (Biden) will probably publicly restate the commitment the U.S. has under the mutual defense treaty and that the islands are covered under article five of the treaty and that we recognize Japan's administrative control and oppose any efforts to undermine that," said Bonnie Glaser, an Asia expert at the Center for Strategic and International Studies think tank. "It's essential that he says that publicly."
U.S., Japanese and South Korean military aircraft all breached the aerial defense zone last week without informing Beijing and China later scrambled fighters into the area.
The military posturing has raised fears of a clash between the United States and its allies and China as it becomes more assertive in the East China Sea and South China Sea under President Xi Jinping.
Two U.S. B-52 bombers flew through the defense zone last week without an immediate response from China, leading some military analysts to conclude that Beijing has overreached.
But, acting on U.S. government advice, three U.S. airlines are notifying Chinese authorities of flight plans when traveling through the zone, even though Washington says this does not mean U.S. acceptance of the zone.
Biden is expected to suggest ways out of the crisis when he meets Xi in Beijing on Wednesday.
"What the Americans can hope to do is to try to tell the Chinese that this ratcheting up is not very clever and is counterproductive and that there is a way out, which is for the Chinese simply to de-emphasize (the defense zone) and not to enforce it," said Jonathan Eyal, director of international security studies at the Royal United Services Institute in London.
Biden often relies on his affability and talent for personal relations when he meets foreign leaders and he feels he has a bond with Xi who he has known since before the Chinese president took office.
"He has a way of saying to somebody, 'I understand the predicament you're in, and far be it from me to tell you what to do, but I'm going to offer some advice,'" said Julie Smith, who was Biden's deputy national security advisor until June.
"Because he's got this personal relationship with Xi, they take him very seriously," Smith said. "They view him as an honest broker."
All the same, Biden's well-known frankness can go too far and he upset Chinese students at a speech at the University of Pennsylvania in May when he told them China's communist system does not allow them to "think different."
An immediate resolution to the air defense zone dispute is unlikely, said Jia Qingguo, professor and associate dean of the School of International Studies at Peking University.
(Read more: US, Japan slam China airspace rules on islands)
"China will probably say to Biden that this is a standard practice for more than 20 countries. Why the fuss?"
"It is helpful for the two sides to gauge each other's intentions and clarify issues and develop some kind of understanding as to what to expect. But this issue will probably linger on. It is good for Biden to come at this time so that this issue gets discussed at a high level. Other issues need attention too," Jia said.
Despite the military standoff, U.S. officials see increased cooperation on a range of issues from climate change to North Korea's nuclear weapons ambitions a year after Xi took over the helm of the Communist Party.
It is not clear whether Biden will ask for Chinese help in pressuring North Korea to release U.S. war veteran Merrill Newman, 85, who it arrested last month.
The Biden visit goes some way to addressing concerns among U.S. allies in Asia that Washington is neglecting the region because of budget fights at home, Iran nuclear talks and the Syrian civil war.
Obama canceled a trip to Southeast Asia in October because of the partial U.S. government shutdown, and a much vaunted "pivot to Asia," a strategic rebalancing of U.S. priorities toward the Pacific, has yet to show many results.
(Read more: Adapt Now: Japan firms heed message in China dispute)
Obama's national security adviser, Susan Rice, announced in November that Obama would travel to Asia in April to make up for the canceled visit.
"The fact that (Biden's) visit encompasses both America's allies and America's chief rival in the region is intended to show that the United States is the only power able to maintain the balance in the region, which is absolutely what the pivot was all about," said Eyal, of the Royal United Services Institute.
He said "a prevalent mood in Asia that the administration hasn't got the stomach for military action and is disinterested in Asia" may have propelled China to announcing its defense zone.