WASHINGTON — In order to operate in the Arctic, the U.S. military must spend more money on joint training and cold weather technology and more time on Alaska’s ranges and working with Native American tribes, according to defense officials.

U.S. defense officials announced at the Sea Air Space forum here on Monday that September Arctic sea ice is receding at a rate of roughly 13 percent per decade. That presents economic opportunities for nations with coastlines that hug the region but also competition from rivals.

Russian forces are projecting power within the Arctic, operating the world’s largest icebreaker fleet while building out air bases, sea ports, weapons and domain awareness tools to operate there.

China also has declared itself a “near-Arctic state" as it angles for a share of the trillions of dollars to be made off minerals, natural gas, ocean fisheries and trade routes in the region.

“I’m not sure that’s even a defined term,” U.S. Air Force Gen. Terrence O’Shaughnessy said of China’s self-designated title.

O’Shaughnessy, who helms both U.S. Northern Command and North American Aerospace Defense Command, said that enforcing a “rules-based international order” is at the forefront of U.S. policy. But the security implications of a warming Arctic are clear: the U.S. homeland is no longer a sanctuary.

“The Arctic is the first line of defense,” O’Shaughnessy said.