U. S. President Barack Obama says developments in the Asia-Pacific region will largely define the century ahead and that the U.S. presence there is his administration's top priority.

President Obama told Australian lawmakers Thursday that the United States is a Pacific power and will always be one. He said the region will have a role in creating jobs and opportunity for the American people and he stressed that any reductions in U.S. defense spending will not come at the expense of that part of the world.

The U.S. president addressed the Australian Parliament on the second day of his visit to the country. On Wednesday, Mr. Obama and Australia's prime Minister Julia Gillard announced an agreement to maintain U.S. forces on Australian soil.

China reacted swiftly to the announcement in Canberra, suggesting the deployment of U.S. troops to Australia may not be appropriate and should be discussed within the international community.

In his speech, Mr. Obama insisted there was nothing inappropriate about the plan. Mr. Obama said the U.S. troop presence will provide new opportunities to train with U.S. allies and partners and to respond to a full range of challenges, including humanitarian crises and disaster relief.

He said the United States welcomes the rise of a peaceful and prosperous China and will seek more opportunities to work with Beijing, including greater communication between each other's militaries to promote understanding.

The troop deployment deal calls for a force of 200 to 250 U.S. Marines to be based in Australia's Northern Territory for rotating six-month deployments. The contingent would grow over time to a full force of 2,500 personnel.

In addition, Australia has agreed to facilitate greater use of Darwin air base by U.S. military aircraft, including jet fighters and bombers. The two sides also agreed to boost the use of Western Australia's Stirling naval base by U.S. vessels.

In his speech, Mr. Obama also said human rights violations persist in Burma despite progress there, and said the United States will continue to speak clearly about the steps that must be taken for Burma's government to have a better relationship with the United States.

He said the United States and Australia seek an open international economic system where rules are clear and every nation plays by them.

Later Thursday, Mr. Obama visits Australia's air base in Darwin, becoming the first U.S. president to do so. He stopped in Australia on the way to Bali, Indonesia, where he and Ms. Gillard will attend the East Asia Summit. The United States as well as Russia will participate in the summit as full members for the first time.