The decision to remove troops defending South Korea dramatically underscored the strains that have been placed on the US Army as it fights Iraqi insurgents.

Pentagon officials, however, said "the relocation" of the 2nd Brigade, 2nd Infantry Division to Iraq was part of a global realignment of US forces that has been under discussion with South Korea and Japan for over a year.

They stressed it would result in "no diminution of capabilities either in the region or on the Korean peninsula."

"Due to our strengthened posture and the ability to quickly reinforce capabilities throughout the region, we can deploy forces from Korea without assuming additional operational risks," said Richard Lawless, deputy under secretary of defense for Asia Pacific policy.

"The United States has the capability to quickly augment air and naval presence in the Asia Pacific region," he said.

No decision had been made on whether the brigade would return to South Korea after its year-long tour in Iraq, the officials said.

"When we look at it a few months from now, we'll decide whether it makes more sense for those troops to come back to South Korea or to go somewhere else," said Lieutenant Commander Flex Plexico, a Pentagon spokesman.

The move will reduce the number of US ground troops in South Korea to 34,000, the official said, the first time the level has fallen below about 37,000 since early 1990s.

Asked whether the move might be read by North Korea as a sign that the US was tied down in Iraq, a senior military official said, "That would be a misperception, let's put it that way."

President George Bush discussed the plans on Monday with South Korean President Roh Moo-Hyun and Japanese Prime Minister Junichiro Koizumi, both of whom expressed their "support and understanding," the White House said.

The 2nd Infantry Division's 2nd Brigade was notified over the weekend that it will begin deploying to Iraq in mid-summer, said a senior military official, who asked not to be identified.

How much of the brigade's M-1 Abrams battle tanks, Bradley fighting vehicles and other vehicles will go with them was still being worked out.

The order means that some brigade members will be away from home for as long as 18 months to two years, and most will be away for 12 to 18 months, the senior military official said. That is well beyond the year limit the Pentagon had promised.

"That is needed in this case and it reflects the fact that we are at war," the military official said.

The officials said the brigade was selected because it had not yet pulled a tour in either Afghanistan or Iraq, and was one of the best trained and most ready units in the army.

The Pentagon decided earlier this month to maintain force levels in Iraq at about 138,000, scrapping plans to reduce the size of the force there because of a surge in violence as the US-led coalition moves to handover sovereignty to Iraqis.

Deployment orders so far have gone to only about half the 20,000 additional combat troops that are needed to maintain a beefed up military presence in Iraq.

Units that already have received deployment orders are a brigade of the army's 10th Mountain Division and two US marine expeditionary units.

On May 4, when those movements were announced, top generals acknowledged that the deployment plans carried risks for the US military's capacity to respond to crises in parts of the world like the Korean peninsula.

The army said a brigade of the 82nd Airborne Division would be ready for such contingencies, however.

For its part, Seoul is seeking assurances that the 4,000 troops will return once their Iraq mission is concluded and that their absence would not reduce the deterrent capability of forces deployed here, South Korean officials said.

South Korea has vigorously opposed any reduction in US troops, which historically have served as a tripwire that would guarantee immediate US military involvement if North Korea were to go to war with the south.

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