President Obama insisted Wednesday that the United States does not fear China, even as U.S. officials acknowledged that a rising China is part of the reason for a new U.S.-Australia security pact created in response to Beijing's growing aggressiveness.

The plan is to have a Marine, air and ground task force using Australian facilities to act as a "force multiplier" in the region. No new U.S. bases will be built. Marines will rotate into and out of the region, building up slowly from 250. After the buildup is complete, they will total some 2,500.

The number and frequency of U.S. aircraft using Australian air bases will increase and more bases will be in use. However, no numbers were given regarding air power, there is no ships element in this agreement.

Obama called the deployment "significant," and said it would build capacity and cooperation between the U.S. and Australia.

"It also allows us to meet the demands of a lot of partners in the region that want to feel that they're getting the training, they're getting the exercises, and that we have the presence that's necessary to maintain the security architecture in the region," Obama said.

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U.S. officials were careful to emphasize that the pact was not an attempt to create a permanent American military presence in Australia.

But China responded swiftly to the president's announcement during a joint news conference with Australian Prime Minister Julia Gillard. Foreign Ministry spokesman Liu Weimin warned that an expanded U.S. military footprint in Australia may not be appropriate and deserved greater scrutiny. Liu added that it was worth discussing whether the plan was in line with the common interests of the international community.

Asked about China's reaction, National Security Council spokesman Ben Rhodes responded simply by saying, we think it's appropriate. Rhodes said that the "sustained" presence it is a response to the demand from nations in the region that have signaled they want the U.S. to be present.

The president spoke shortly after arriving in the Australian capital, his second stop on a nine-day tour of the Asia-Pacific region. After a 10-hour flight from Honolulu, where he hosted an economic summit, Obama headed straight into meetings with Gillard.

On Thursday, Obama will address the Australian Parliament, then fly to the northern city of Darwin, where some of the Marines deploying to Australia next year will be based.

During his news conference with Gillard, the president sidestepped questions about whether the security agreement was aimed at containing China. But he said the U.S. would keep sending a clear message that China needs to accept the responsibilities that come with being a world power.

"It's important for them to play by the rules of the road," he said.

And he insisted that the U.S is not fearful of China's rise.

"I think the notion that we fear China is mistaken. The notion that we're looking to exclude China is mistaken," he said.

The U.S. and smaller Asian nations have grown increasingly concerned about China claiming dominion over vast areas of the Pacific that the U.S. considers international waters, and reigniting old territorial disputes, including confrontations over the South China Sea. China's defense spending has increased threefold since the 1990s to about $160 billion last year, and its military has recently tested a new stealth jet fighter and launched its first aircraft carrier.

Defense Secretary Leon Panetta has said that the goal of the new security pact is to signal that the U.S. and Australia will stick together in face of any threats.

The only American base currently in Australia is the secretive joint Australia-U.S. intelligence and communications complex at Pine Gap in central Australia. But hundreds of U.S. service personnel are based in Australia on exchange.

Air combat units also use the expansive live bombing ranges in Australia's sparsely populated north in training rotations of a few months and occasionally naval units train off the coast. But training exercises involving ground forces are unusual.

During Wednesday's brief news conference, Obama and Gillard also fielded questions on a range of other issues, from U.S. efforts to address climate change to the debt crisis in Europe.

Obama reiterated his call for urgent action by European leaders to back the euro and develop a financial firewall to keep the threat of default facing Greece and Italy from spreading across the Eurozone.

"The problem right now is one of political will, it's not a technical problem," Obama said. "At this point, the larger European community has to stand behind the European project."

Asked whether the U.S. would be able to lower carbon emissions through a cap-and-trade system as Australia is undertaking, Obama conceded the U.S. has been unable to pass such a plan through Congress, but noted U.S. efforts to increase vehicle fuel efficiency and to explore clear energy options. He said emerging economies such as India and China must also assume responsibility for addressing climate change.

For Obama and Australia, the third time's the charm. He canceled two earlier visits, once to stay in Washington to lobby for passage of his health care bill, and again in the wake of the oil spill in the Gulf of Mexico.

"I was determined to come for a simple reason: The United States of America has no stronger ally than Australia," he said.

The Associated Press contributed to this report.