Hagel spoke at a news conference in Sydney with Australian Defense Minister David Johnston.
The document re-emphasizes America's rebalance to the Asia-Pacific, Hagel said, adding that it will be invaluable to sustaining a peace and stability throughout the region.
The cornerstone of the document is the rotational presence of U.S. Marines in Darwin and American airmen in Northern Australia, Hagel said, noting that this will allow the militaries to work more closely together.
"It will expand our regional cooperation here in the Asia-Pacific from engagement with [the Association of Southeast Asian Nations] to the trilateral cooperation that we have been working on with Japan," the defense secretary said.
The agreement looks long-term at joint military capacity building, cooperation in humanitarian assistance and disaster relief, and other new initiatives.
The agreement is part of the Australia-U.S. ministerial conference. The two defense leaders will be joined in the discussions by Secretary of State John F. Kerry and Australian Foreign Affairs Minister Julie Bishop. Army Gen. Martin E. Dempsey, the chairman of the Joint Chiefs of Staff, also is participating.
Those talks will look at maritime security, special forces, missile defense and Afghanistan. They also will involve discussion of the situation in Ukraine, Hagel said.
"We'll also be conferring on the threat posed by [the Islamic State of Iraq and the Levant] in Iraq and America's appreciation to Australia, in particular, for Australia's offer to assist in humanitarian relief operations there," he added.
Hagel took the opportunity to highlight America's rebalance effort. The United States has been and will remain a Pacific power, he said. About 200 U.S. Navy ships are now in the region, along with more than 360,000 uniformed and civilian personnel.
"It's pretty clear that the U.S. is committed to this part of the world, but also does not mean a retreat from any other part of the world," Hagel said. "We have interests all over the world. We'll continue to work with our partners and strengthen those partnerships and the alliances we have in every part of the world and here as well."
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