President Barack Obama insisted Wednesday that the notion that the United States fears China or wants to exclude the growing power from American economic alliances in the Asia-Pacific region is mistaken.

But he said the United States will 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," Obama said during a joint news conference with Australian Prime Minister Julia Gillard.

Obama and Gillard announced a joint security pact that would increase U.S. military presence in Australia, a move widely viewed as an attempt to address China's growing aggressiveness in the region. About 250 U.S. Marines with begin a rotation in northern Australia starting next year, with a full force of 2,500 military personnel staffing up over the next several years.

"This rotational deployment is significant because what it allows us to do is to not only build capacity and cooperation between our two countries, but 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.

Officials in both countries have emphasized that the agreement does not create a permanent U.S. presence or military base in Australia.

Obama sidestepped questions about whether the security agreement was a direct attempt to counter China's growing military aggressiveness. But the U.S. and smaller Asian nations have growing 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.

Obama arrived in Australia Wednesday afternoon following the Asia-Pacific economic summit he hosted in Hawaii last week. A central part of the summit was an agreement for a transpacific trade bloc that includes eight countries in addition to the United States.

The agreement sets standard rules for commerce. Obama said that while the U.S. is not intentionally excluding China from the agreement, joining the pact with require Beijing "to rethink some of its approaches to trade."

The U.S. has accused China of undervaluing its currency to Chinese exports cheaper and U.S. exports to China more expensive. China had a $273 billion trade surplus with the U.S. last year and U.S. lawmakers say the imbalance hurts American manufacturers while taking away American jobs.

U.S. officials have also pressed China to end unfair discrimination against the U.S. and other foreign countries and to end to measures that undercut its intellectual property.