According to the Yonhap news agency in Seoul on Wednesday, the revised plan is to remove 12,500 US soldiers by 2008.
Quoting a defence source, the new plan means 5000 soldiers will be withdrawn before December this year, with most of those transferred immediately to Iraq.
Next year, 3000 more will leave, followed by 2000 in 2006 and 2500 in 2007 and 2008, the news agency said.
Washington said in June it would withdraw a third of its troops by the end of next year as part of a global troop redeployment plan.
The US military also reversed its decision to pull out its Multiple Launch Rocket System batteries and Apache attack helicopters deployed near the border with North Korea.
The White House has said its troop reduction will not weaken deterrence against North Korea, citing an $11 billion programme to build up firepower of US troops there over the next few years.