The United States and Australia are planning a major expansion of military ties, including possible drone flights from a coral atoll in the Indian Ocean and increased U.S. naval access to Australian ports, as the Pentagon looks to shift its forces closer to Southeast Asia, officials from both countries said.

The moves, which are under discussion but have drawn strong interest from both sides, would come on top of an agreement announced by President Obama and Prime Minister Julia Gillard in November to deploy up to 2,500 U.S. Marines to Darwin, on Australia’s northern coast.

The talks are the latest indicator of how the Obama administration is rapidly turning its strategic attention to Asia as it winds down a costly decade of war in Afghanistan and Iraq. The U.S. government is finalizing a deal to station four warships in Singapore and has opened negotiations with the Philippines about boosting its military presence there. To a lesser degree, the Pentagon is also seeking to upgrade military relations with Thailand, Vietnam, Malaysia, Indonesia and Brunei.

Although U.S. officials say the regional pivot is not aimed at any single country, analysts said it is a clear response to a rising China, whose growing military strength and assertive territorial claims have pushed other Asian nations to reach out to Washington.

The Pentagon is reviewing the size and distribution of its forces in northeast Asia, where they are concentrated on Cold War-era bases in Japan and South Korea. The intent is to gradually reduce the U.S. military presence in those countries while enhancing it in Southeast Asia, home to the world’s busiest shipping lanes and to growing international competition to tap into vast undersea oil and gas fields.

“In terms of your overall influence in the Asia-Pacific zone, the strategic weight is shifting south,” said a senior Australian official who spoke on the condition of anonymity to discuss the military talks. “Australia didn’t look all that important during the Cold War. But Australia looks much more important if your fascination is really with the Southeast Asian archipelago.”

Australia is a long-standing ally of the United States, and one of its closest partners in intelligence and military matters. More than 20,000 Australian troops spent time in Iraq between 2003 and 2009. About 1,500 Australian troops are now in Afghanistan as part of the NATO-led coalition.

An official interim review of Australia’s military basing structure recently concluded that the chances of the country coming under direct military attack are “currently remote.”

But it urged the government to strengthen its forces along the northern and western coasts, near where most of its mineral wealth is concentrated and where its defenses are relatively sparse. Australia is blessed with an abundance of natural resources and has become China’s leading supplier of coal and iron ore.

The strategic review also advises the government to tailor its basing plans by considering U.S. security interests.

For instance, the review urges a major expansion of the Stirling naval base in Perth, its primary port in western Australia, noting that the installation“could also be used for deployments and operations in Southeast Asia and the Indian Ocean by the U.S. Navy.”

Specifically, the review suggests that Stirling be upgraded in part so it could service U.S. aircraft carriers, other large surface warships and attack submarines.

President Barack Obama addresses Australian troops and U.S. Marines with Australian Prime Minister Julia Gillard at a base in Australia in November. (JIM WATSON/AFP/GETTY IMAGES)

Australian officials said a decision about Stirling’s future is not imminent, but the Pentagon’s interest has intensified recently. Navy Secretary Ray Mabus is scheduled to visit Perth and Darwin this month, following up on a February visit to Australia by Adm. Mark Ferguson, the vice chief of naval operations.

“The Australians have been one of our oldest, strongest allies,” Mabus said in an interview. “It’s fair to say that we will always take an interest in what the Australians are doing and want to do.”

Perth’s drawback is its isolation. It is about 2,400 miles south of Singapore, and 1,600 miles southwest of Darwin. But Pentagon officials say they are looking at the location because it could give the Navy a sorely needed place to refuel, re-equip and repair ships on the Indian Ocean.

“Australia is the only ally that we have on the Indian Ocean,” said a senior U.S. defense official, who spoke on the condition of anonymity to discuss strategic planning. “We see the Indian Ocean as an area that we need to spend a little more time on, where we have fewer well developed relations with countries, compared to the western Pacific.”

Elsewhere in the Indian Ocean, the United States operates a key joint naval and air base on the British island territory of Diego Garcia, about 1,000 miles south of the tip of India. But U.S. officials said operations are crowded, with little room to expand. In addition, the base’s future is uncertain; the U.S. lease will expire in 2016.

Partly as a result, U.S. officials are eyeing another coral atoll 1,700 miles to the east: the Cocos Islands, a remote Australian territory.

U.S. and Australian officials said the atoll could be an ideal site not only for manned U.S. surveillance aircraft but for Global Hawks, an unarmed, high-altitude surveillance drone. The U.S. Navy is developing a newer version of the Global Hawk, known as the Broad Area Maritime Surveillance drone, or BAMS, that is scheduled to become operational in 2015. Aircraft based in the Cocos would be well-positioned to launch spy flights over the South China Sea.

Pentagon officials said they are intrigued by the potential offered by Perth and the Cocos Islands, as well as another Australian proposal to build a new fleet base at Brisbane, on the east coast. But U.S. officials cautioned that nothing has been decided.

They also emphasized that the U.S. military is interested in operating only as a guest and is not seeking to develop its own bases.

Peter Leahy, a former Australian army chief, said the agreement to deploy U.S. Marines in Darwin is the first step as the military partnership expands.

“I think the discussions are well advanced and will lead to quite substantial arrangements,” said Leahy, now director of the National Security Institute at the University of Canberra. “Marines are important and I love them dearly, but the decisive plays in this region will come from the Navy and Air Force.”

Hugh White, a former Australian defense official, said that the Australian security alliance with the United States is essential but that Beijing could perceive the moves as too bellicose.

“This is all about China, of course,” said White, a professor of strategic studies at Australian National University in Canberra. “Australia is in a very complicated position in this. None of us want to live in an Asia dominated by China, but none of us want to have an adversarial relationship with China.”

In November, some influential Chinese voices criticized the deal to bring Marines to Darwin, with the state-run People’s Daily warning that Australia could be “caught in the crossfire” if it allowed the U.S. military to harm China’s interests.

Australian officials have played down such talk as predictable rhetoric.

“From our point of view, we want the Chinese not to be sensitive,” said the senior Australian official. “But having said that, they also understand that the relationship between the United States and Australia predates any American concern with them. China accepts that Australia does things with the U.S.”