Washington ? The cost of a long-term U.S. military presence in Iraq similar to the peacekeeping role American troops have played in South Korea would range from $10 billion to $25 billion a year, the Congressional Budget Office said Thursday.

A Korea-like presence of 55,000 troops would cost about $25 billion a year in a “combat” scenario similar to the current mission, the nonpartisan CBO said in a report.

Keeping the troops protected at established military bases and out of combat would lower the cost to about $10 billion annually. One-time costs for base construction or additional equipment could reach $8 billion, the CBO said.

Senate Budget Committee Chairman Kent Conrad, D-N.D., requested the study after President Bush likened America’s future in Iraq to the peacekeeping role U.S. troops play in South Korea, where they have been stationed for some five decades.

Congress has already appropriated $412 billion for the Iraq mission, CBO says, with costs for operations there and in Afghanistan expected to require an almost $200 billion additional appropriation for the budget year beginning Oct. 1.

“The Bush administration has been trying to hide the cost of this war every step of the way,” Conrad said. “Now the president is considering a significant ongoing presence in Iraq, long after he leaves office.”