Myanmar's democratization has led to rare bipartisanship in the U.S. capital. Republican Senate Minority Leader Mitch McConnell of Kentucky, who has had a longstanding interest in the Asian country, commended Obama for scheduling the trip.
"I think it's an important step for him to take," McConnell said.
In Cambodia, also a first visit for a sitting U.S. president, Obama will participate in the East Asia Summit, which includes the 10-member Association of Southeast Asian Nations and eight other nations: the United States, China, Japan, South Korea, India, Russia, Australia and New Zealand.
Obama will hold separate one-on-one meetings with outgoing Chinese Premier Wen Jiabao and Japanese Prime Minister Yoshihiko Noda.
Those meetings come amid territorial disputes in the region, including rival claims by China, the Philippines and Vietnam to South China Sea islands and disputed East China Sea islands controlled by Japan.
The trip is not without controversy.
Human rights groups have argued that Obama's trip to Myanmar is premature and that, in seeking to find allies in the region, Obama has been less attentive to repressive regimes such as that of Cambodia's longtime Prime Minister Hun Sen.
Obama aides acknowledge that Myanmar can still do better and say Obama will raise U.S. concerns about Cambodia's crackdowns on dissidents and civil society groups in the meeting with Hun Sen.
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.