AS MYANMAR EASES CONTROLS, U.S. SEES DIPLOMATIC OPENING

[Indeed, China’s prime minister, Wen Jiabao, warned the United States on Friday to steer clear of territorial disputes between China and its neighbors, saying they ought to be resolved directly “through friendly consultations.” And the Chinese Foreign Ministry expressed concern about the political changes in Myanmar, saying it hoped they would not destabilize the country.]

By Thomas Fuller And Mark Landler

Aung San Suu Kyi

BANGKOK — The long-isolated nation of Myanmar embarked on a potentially decisive shift in direction on Friday, as its main opposition leader, Daw Aung San Suu Kyi, agreed to rejoin the country’s political system and Hillary Rodham Clinton prepared to become the first secretary of state and highest-ranking American to visit the country in half a century.

The confluence of events, though weeks in the making, unfolded with dramatic speed during a tour of Southeast Asia by President Obama, and underscored the central message of the president’s trip: that the United States intended to reassert itself in the Asia-Pacific region to limit the influence of a rising China.

Under decades of military rule, Myanmar, also known as Burma, counted neighboring China as its primary ally and economic partner. But a new cast of leaders there has begun to ease political controls, court the opposition and repair relations with Western and other Asian powers, an opportunity the Obama administration has eagerly embraced.

Combined with the announcements this week that the United States would station 2,500 Marines in Australia and that it intended toenhance military ties with the Philippines, Mr. Obama’s decision to send Mrs. Clinton to Myanmar next month clearly rattled Beijing, which has issued a series of warnings claiming that the United States is seeking to destabilize the political and military situation in the region.

“We are seeing a very significant new phase in U.S. policy toward China,” said Kenneth G. Lieberthal, a top China adviser in the Clinton administration, “a much more active, integrated, assertive U.S. posture in Asia than anyone expected six months ago.”

For Mrs. Aung San Suu Kyi, the decision to reregister her party and compete in elections in the military-backed system represents a historic shift. Known globally as a symbol of endurance in the face of dictatorship, she has spent most of her 23 years in politics battling the country’s generals, much of that time in prison or under house arrest. Now she is joining the system they created.

The civilian government that took power in March is dominated by former generals, including President Thein Sein. It has sought to liberalize Myanmar’s moribund economy and pushed the country toward a more open political system, wooing Mrs. Aung San Suu Kyi in a carefully choreographed rapprochement.

In announcing Mrs. Clinton’s plans to visit, Mr. Obama cited “flickers of progress” in the country. The United States, he said, remains concerned about human rights abuses, the persecution of democratic reformers and brutality toward ethnic minorities.

But he hailed policies by Mr. Thein Sein as leading the country “on the path toward reform.” He cited the government’s cooperation with Mrs. Aung San Suu Kyi, the release of political prisoners and the relaxation of media restrictions. “These are the most important steps toward reform in Burma that we’ve seen in years,” Mr. Obama said.

The subtext is that Myanmar has unexpectedly become a kind of diplomatic prize for the United States, which is eager to show its traditional allies in Asia, including Japan, South Korea, Australia, the Philippines and Thailand, that it is no longer distracted by the wars in Iraq and Afghanistan and that it is advancing democratic interests, promoting free-market economic reform and counterbalancing the power of authoritarian China.

While Mr. Obama traveled to Australia to seal an arrangement to base Marines there, Mrs. Clinton signed a declaration with the Philippines on the deck of an American destroyer that called for disputes over maritime claims in the South China Sea to be settled through a “multilateral” process — something China has flatly rejected and a term the United States avoided when it first waded into the South China Sea dispute in July 2010.

She also somewhat provocatively referred to the South China Sea as the West Philippine Sea, a term preferred in the Philippines but reviled in Beijing.

Such moves, added together, may prompt broader alarm in China. “With their mind-set, whatever you do, it may be considered part of a conspiracy,” said Cheng Li, a senior fellow at the Brookings Institution.

Some China watchers say the American moves may feed suspicions in China that the United States is seeking to encircle it because it is uneasy with having an economic and military rival.

Indeed, China’s prime minister, Wen Jiabao, warned the United States on Friday to steer clear of territorial disputes between China and its neighbors, saying they ought to be resolved directly “through friendly consultations.” And the Chinese Foreign Ministry expressed concern about the political changes in Myanmar, saying it hoped they would not destabilize the country.

In September, China aimed its anger at Myanmar after it suspended a Chinese-led project to build a hydroelectric dam in northern Myanmar, creating a rare rift between the countries.

This tension helps explain Myanmar’s openness to dealing with the United States, which was itself eager to expand its presence in the region — as Mrs. Clinton articulated in an article published this month in Foreign Policy magazine titled “America’s Pacific Century.”

“As the war in Iraq winds down and America begins to withdraw its forces from Afghanistan, the United States stands at a pivot point,” Mrs. Clinton wrote in the article. The United States should resist the temptation of downsizing its “foreign engagement” after the wars, she said, because engagement in Asia “is critical to America’s future.”

Administration officials say they are trying to bring China into the club of responsible great powers. Mrs. Clinton; Thomas E. Donilon, the national security adviser; and others have labored, with mixed results, to enlist China in problems like climate change, global economic imbalances and renegade nuclear programs in Iran and North Korea.

But progress is halting, officials admit. A senior administration official described China as a “peculiar adolescent that can no longer hide behind its status as a developing nation, but does not see itself with the full responsibility of a global power.”

Closer ties to the United States would bring Myanmar full circle to its years immediately after independence from Britain in 1948. At the time Myanmar sought close ties with the West to balance relations with China, said Thant Myint-U, a historian and former United Nations official.

In recent years, China has become one of Myanmar’s largest trade partners, lured by bountiful natural resources. Myanmar has relied on China for much-needed investment, partly to mitigate the effects of Western sanctions.

Yet anti-Chinese sentiment has flared up periodically in Myanmar’s history, and observers said resentment at China’s plans to consume nearly all of the power from the halted dam was one reason the plan was so unpopular.

Aung Din, the executive director of the U.S. Campaign for Burma, a pressure group that supports Myanmar’s democracy movement, says he saw the seeds of backlash against Chinese interests in Myanmar. “Many projects are carried out by Chinese companies; prominent businessmen are Chinese; everything belongs to China, actually,” he said. “If we don’t take any action, Burma will become a satellite state of China.”

Mrs. Clinton’s visit, he said, might encourage the Burmese government and people “to confront Chinese interests.”

Thomas Fuller reported from Bangkok, and Mark Landler from Washington.

This article has been revised to reflect the following correction:

Correction: November 18, 2011

Due to an editing error, an earlier version of this article gave the wrong city as Myanmar’s capital. It is Naypyidaw, not Yangon.

@ The NewYork Times