An emerging defense agreement would let the U.S. expand its military presence in Australia as the Obama administration and its allies maneuver to counter an increasingly assertive China.
It would include positioning U.S. equipment in Australia, increasing access to bases and conducting more joint exercises and training.
The arrangement, somewhat controversial in Australia, is expected to be a centerpiece of President Barack Obama's visit to the country in November.
Australian Defense Minister Stephen Smith said the broader cooperation will mean "more ships in, ships out; more planes in, planes out; more troops in, troops out."
The U.S. and Australia expect to finalize the plan later this year, according to a senior defense official who spoke on condition of anonymity because the arrangement was not complete.
Defense Secretary Leon Panetta and Secretary of State Hillary Rodham Clinton met Thursday with Australian defense chief Stephen Smith and Foreign Minister Kevin Rudd for talks on the basing arrangement, military cooperation in the Pacific region and other issues.
Afterward, Smith said the goal of the deeper defense arrangement is to "make very clear to those who would threaten us that we are going to stick together." He did not mention China specifically, although it poses the most potent military force that could oppose the U.S. and Australia in the Pacific.
U.S. officials deny that closer U.S. cooperation with Australian and Southeast Asian nations is meant as a challenge to China, which claims dominion over vast areas of the Pacific that the U.S. considers international waters. China also has alarmed smaller Asian neighbors by reigniting old territorial disputes.
The U.S. claims a national security interest in protecting crucial international shipping lanes; China calls it meddling. Beijing rebuffed a proposal that Clinton made last week to host talks between China and Japan over one such dispute.
Afghanistan was also a major topic, given that Australia is the largest contributor of troops to the war effort outside NATO countries, as was the unrest in the Middle East.
U.S. officials said they are not looking to establish any American bases in Australia, but want increased military access and cooperation that will allow the U.S. to broaden its posture in the region.
The shared base idea is part of U.S. efforts to diversify its Asian military stance, which long has focused on northern Asia. Australian bases would place U.S. forces or assets such as ships and planes much closer to potential natural disasters or conflicts in the Southern Hemisphere.
Separately, U.S. and Australian officials have decided to include cooperation on cybersecurity as part of their defense treaty. It's the first time that the Obama administration has carved out that kind of partnership with a country outside NATO.
The agreement is partly in response to the cyberthreat emanating from the Pacific region, especially China and North Korea.
The U.S. and Australia have conducted more than a dozen joint exercises in 2010 and 2011, including the massive Talisman Sabre drill that involves 15,000 U.S. troops, U.S. officials said.
U.S. foreign military sales with Australia were more than $3.7 billion this year, as of early July. They include the purchase of C-17 cargo aircraft, Joint Strike Fighters, as well as other combat and maritime aircraft.