



HANOI, Vietnam — China’s military expansion and assertive trade policies have set off jitters across Asia, prompting many of its neighbors to rekindle old alliances and cultivate new ones to better defend their interests against the rising superpower.

A whirl of deal-making and diplomacy, from Tokyo to New Delhi, is giving the United States an opportunity to reassert itself in a region where its eclipse by China has been viewed as inevitable.

President Obama’s trip to the region this week, his most extensive as president, will take him to the area’s big democracies, India, Indonesia, South Korea and Japan, skirting authoritarian China. Those countries and other neighbors have taken steps, though with varying degrees of candor, to blunt China’s assertiveness in the region.

Mr. Obama and Prime Minister Manmohan Singh of India are expected to sign a landmark deal for American military transport aircraft and are discussing the possible sale of jet fighters, which would escalate the Pentagon’s defense partnership with India to new heights. Japan and India are courting Southeast Asian nations with trade agreements and talk of a “circle of democracy.” Vietnam has a rapidly warming rapport with its old foe, the United States, in large part because its old friend, China, makes broad territorial claims in the South China Sea.