By Caren Bohan and Laura MacInnis
CANBERRA (Reuters) - President Barack Obama said on Thursday that the U.S. military would expand its role in the Asia-Pacific region despite budget cuts, declaring America was "here to stay" as a Pacific power which would help shape the region's future.
China, which has longstanding fears that its growing power could be hobbled by U.S. influence, voiced misgivings about Obama's announcement of a de facto military base in Australia.
Obama acknowledged China's unease at what it sees as attempts by Washington to encircle it, pledging to seek greater cooperation with Beijing.
The U.S. military, turning its focus away from Iraq and Afghanistan, would be more broadly distributed in Asia, particularly Southeast Asia, more flexible and help build regional capacity, he told the Australian parliament.
"As we end today's wars, I have directed my national security team to make our presence and missions in the Asia Pacific a top priority," Obama said in a major speech on Washington's vision for the Asia-Pacific region.
"As a result, reductions in U.S. defense spending will not -I repeat, will not - come at the expense of the Asia Pacific."
He added: "We'll seek more opportunities for cooperation with Beijing, including greater communication between our militaries to promote understanding and avoid miscalculation."
Nervous about China's growing clout, U.S. allies such as Japan and South Korea have sought assurances from the United States that it would be a strong counterweight in the region.
A first step in extending the U.S. military reach into Southeast Asia will see U.S. Marines, naval ships and aircraft deployed to northern Australia from 2012.
That deployment to Australia, which by 2016 will reach a taskforce of 2,500 U.S. troops, is small compared with the 28,000 troops stationed in South Korea and 50,000 in Japan.
But the presence in Darwin, only 820 km (500 miles) from Indonesia, will allow the United States to quickly reach into Southeast Asia and the Indian Ocean.
"It was here in Darwin that our alliance was born during Australia's 'Pearl Harbor'," Obama, with his sleeves rolled up, told 2,000 Australian and U.S. troops in the tropical port, where he stopped off en route to Indonesia.
More bombs were dropped on Darwin during a World War Two Japanese raid than in Hawaii, but Obama said U.S.-Australian troops regrouped and went on to major Pacific victories.
"Here in Darwin and northern Australia we will write the next proud chapter in our alliance," said Obama, adding U.S. and Australian forces would ensure security of the Asian sealanes to the north which were critical for both economies.
The new de facto U.S. base in Australia expands the direct U.S. military presence in Asia beyond South Korea and Japan and into Southeast Asia, an area where China has growing economic and strategic interests.
It will also put more U.S. troops, ships and aircraft much closer to the South China Sea, over which Beijing has sovereignty disputes with several countries.
Obama will raise the issue of the South China Sea during the security East Asia Summit on the Indonesian island of Bali later this week.
CHINA QUESTIONS U.S. DEPLOYMENT TO AUSTRALIA
China has questioned the new U.S. deployment, with a foreign ministry spokesman raising doubts about whether strengthening such alliances helped the region pull together at a time of economic gloom.
But overall its official reaction has been restrained, with an impending leadership succession preoccupying the ruling Communist Party and leaving Beijing anxious to avoid diplomatic fireworks.
Reaction from some state media was harsher, with a commentary from the official news agency Xinhua on Thursday saying that: "Every country in the region...has good reason to question the United States' ambition."
"In fact, it wouldn't come as a surprise if the United States is trying to seek hegemony in the region, which would be in line with its aspirations as a global superpower," said Xinhua.
Indonesia, Southeast Asia's largest country and long wary of any expanded foreign military presence in the region, also warned that Australia deal came with risks.
"What I would hate to see is if such developments were to provoke a reaction and counter-reaction precisely to create a vicious circle of tension and mistrust or distrust," Indonesian Foreign Minister Marty Natalegawa told reporters.
Obama said the United States would seek to work with China to ensure economic prosperity and security in the region, but would speak candidly about issues such as human rights and raise security issues like the South China Sea through which $5 trillion dollars in trade sails annually.
China has broad claims over the sea, also rich in oil, minerals and fishery resources. Vietnam, the Philippines, Taiwan, Malaysia and Brunei hold rival claims that have triggered several disputes in recent years.
U.S. Secretary of State Hillary Clinton pointedly visited the Philippines on Wednesday, saying that no claimant should resort to intimidation to push its cause.
Obama said the increased focus on the Asia-Pacific region was essential for America's economic future.
"As the world's fastest-growing region - and home to more than half the global economy - the Asia Pacific is critical to achieving my highest priority: creating jobs and opportunity for the American people," he said.
(Writing by Michael Perry; Editing by Alex Richardson)