COLORADO SPRINGS, Colo. -- The military is virtually closing the secretive defense complex carved into Cheyenne Mountain that has watched North American skies for missiles for decades.

The North American Aerospace Defense Command operations center will be moved to nearby Peterson Air Force Base, which is home to the U.S. Northern Command created after the Sept. 11 attacks. Both are commanded by Adm. Tim Keating.

In an interview with theDenver Post, Keating said the government's best intelligence "leads us to believe a missile attack from China or Russia is very unlikely."

That, along with the emergence of varied terrorist threats such as suicide bombers "is what recommends to us that we don't need to maintain Cheyenne Mountain in a 24/7 status. We can put it on `warm standby,"' Keating said.

Keating confirmed the move Friday. He said 230 surveillance crew members and an undetermined number of the support staff will make the move within two years.

About 1,100 people now work in the mountain, including 700 support. Buildings inside the mountain, long a symbol of the Cold War, are mounted on springs to absorb the shock from a nuclear blast, while the entrance is guarded by a vault-like door several feet thick.

The complex includes banks of batteries and its own water supply. Excavation on the site began in 1961.

Canadian crews stationed at Cheyenne Mountain will also make the move to Peterson, Keating said.

"Canadians and Americans will be sitting side by side in a joint command center," he said.

Air Force Space Command, which monitors objects in space with a crew of about 100, is looking into moving its operations out of the mountain to Vandenberg Air Force Base in California, which would leave the mountain virtually empty.

Keating said he would like to keep the complex in usable shape, with the goal of being able to bring it online in an hour.

Besides new threats to national security, Keating said practical reasons also came into play.

"I can't be in two places at one time," he said.

Modernizing the Cold War complex has cost more than $700 million since the Sept. 11 attacks, with the work still incomplete, according to a recent congressional hearings.

The underground base was imortalized in several movies including "War Games."