Beijing ? The U.S. military wants to reduce the number of troops based in South Korea by a third in less than two years as part of a global shift in defensive strategies, American and South Korean officials said Monday in Seoul.

The tentative decision to remove about 12,500 military personnel from South Korea appeared to take the government in Seoul by surprise because of the quick pace of withdrawal proposed by the Pentagon. The U.S. plans to reduce its forces to 25,000 from about 37,000 by the end of 2005, but South Korea expected to have several more years before taking on a heavier share of the burden of facing off against North Korea.

American officials emphasized that the reduction in the number of American troops would have no effect on the ability of the U.S. and South Korea to keep the peace or to thwart an attack. The U.S. plans to invest up to $11 billion in the next five years on high-tech weaponry, while South Korea has been steadily positioning its 650,000 armed forces to take over for U.S. troops along the North Korean border.

“Our commitment to our treaty obligations and our ability to fulfill those commitments will remain unchanged,” State Department spokesman Adam Ereli said.

The plan to remove troops from South Korea fits with the strategy developed under Defense Secretary Donald Rumsfeld of realigning American forces into a more flexible fighting force. The Pentagon has proposed withdrawing its two Army divisions from Germany and undertaking an array of other changes in its European-based forces, U.S. and allied officials have told The New York Times. Pentagon policymakers said the aim is to afford maximum flexibility in sending forces to the Middle East, Central Asia and other potential battlegrounds.