PYONGTAEK, South Korea — The cold wind sweeps down from the Siberian steppes across Manchuria and onto the Korean peninsula, thence to brush over a wide expanse of rice paddies on which is being built a huge American military base. From here, expeditions could be launched to any troubled place in Asia.

The conversion of Camp Humphreys, long a small isolated post, into the U.S. Army Garrison Humphreys over the next eight years will turn it, along with the nearby U.S. air base at Osan, into a hub in the consolidation of U.S. forces in South Korea into 47 posts from the present 104 sites.

Of the 28,500 U.S. troops remaining in Korea after recent reductions, 18,000 will be here and another 5,600 in Osan.

The mission of this garrison and the air base will be less focused on the threat from North Korea, which can be met by South Korea's increasingly strong forces, and more on threats elsewhere in this region.

"Our mission is to provide the Army the installation capabilities and services to support expeditionary operations in a time of persistent conflict," said David Frodsham, a senior civilian official overseeing the garrison's expansion.

A senior military officer at U.S. Forces Korea in Seoul said that consolidating American military units into U.S. Army Garrison Humphreys would provide "increased strategic flexibility" to respond to crises elsewhere. The project will cost $13 billion, of which 90 percent is being funded by South Korea to persuade the U.S. to keep its troops here. If the U.S. ever decides to withdraw those forces, the South Koreans would inherit the modern base.

These changes in Korea are part of a realignment of U.S. forces throughout the Pacific. Nearly half of the 17,000 Marines in Okinawa, Japan, are to be moved to Guam. That central Pacific island, which is U.S. territory, is being built into a major air and naval base. A small base in Singapore is coming in for more use, U.S. forces train more in Australia, and the U.S. hopes someday to gain access to Indonesian bases.

Over the next few years, the headquarters of the United Nations Command led by an American four-star general will move here from Seoul as will the headquarters of U.S. Forces Korea and those of its Army, Navy, Marine Corps, and special operations components. The Air Force headquarters is already in Osan. The U.N. command has been here since it fought the Korean War of 1950-53.

The Army's 2nd Infantry Division, its brigade combat team, artillery, helicopter and other units will move from posts north of Seoul to this garrison 55 miles south of Seoul and 85 miles from the demilitarized zone that divides North and South Korea. So will a long list of intelligence, signal, medical, engineering, and logistics units.

The date around which many moves are planned is April 2012, when South Korea assumes wartime operational control of its forces now under a combined U.S.-South Korea command, which will free U.S. forces to concentrate on contingency plans elsewhere. South Korea already has peacetime operational control of its troops.

In Pyongtaek, U.S. Army engineers have undertaken what they say is their largest project ever. The size of the post is to be tripled, to 3,600 acres. Since the expansion lies in a flood plain barely above sea level, the engineers have begun covering it with dirt to raise the plain eight feet that will be protected by a levee ten feet high. In all, it will take 1 million loads in dump trucks to complete the task.

The new post must accommodate the troops, headquarters, motor pools, and firing ranges, plus 35,000 members of families expected here. Until now, troop tours in Korea have been for one year, unaccompanied by families. That is being extended to three years accompanied by families, which requires new housing, schools, medical clinics, sports fields and movie theaters.

The engineers are building high-rise offices for commanders, barracks for troops, and buildings with spacious family apartments. That housing, plus recreational facilities that include a gym with basketball courts worthy of the pros, an Olympic swimming pool, and world class exercise equipment, are intended to make Pyongtaek a choice assignment.

Richard Halloran, formerly with The New York Times as a foreign correspondent in Asia and military correspondent in Washington, is a freelance writer in Honolulu.