FARGO, N.D. -- Democrat Barack Obama opened the door yesterday to refining his plan to bring U.S. troops home from Iraq based on what he hears from military commanders during his coming trip there.

"I am going to do a thorough assessment when I'm there," he told reporters. "I'm sure I'll have more information and continue to refine my policy."

During his presidential campaign, Obama has gone from the hard-edged, vocal opposition to Iraq that defined his early candidacy to more nuanced rhetoric that calls for a phased-out drawdown of combat brigades that, at a rate of one or two a month, could last 16 months. He has said that if al-Qaida builds bases in Iraq, he would keep troops in the region to carry out "targeted strikes."

He said he is saying now what he always has: The war was a mistake and needs to be brought to "a responsible end," but "we need to be as careful getting out as we were careless getting in." This means, he said, that his 16-month timeline "was always premised on" not endangering U.S. troops or Iraq's stability, which commanders said was possible.

Obama's Web site contains this direct promise: "Obama will immediately begin to remove our troops from Iraq. He will remove one to two combat brigades each month, and have all of our combat brigades out of Iraq within 16 months. Obama will make it clear that we will not build any permanent bases in Iraq. He will keep some troops in Iraq to protect our embassy and diplomats; if al-Qaida attempts to build a base within Iraq, he will keep troops in Iraq or elsewhere in the region to carry out targeted strikes on al-Qaida."

Yesterday Obama called it "pure speculation" to suggest he has been softening his position as violence lessens in Iraq.

"I continue to believe that it is a strategic error for us to maintain a long-term occupation in Iraq at a time when conditions in Afghanistan are worsening, al-Qaida is continuing to establish bases in areas of northwest Pakistan, resources there are severely strained, and we are spending $10 to $12 billion a month in Iraq that we desperately need here at home," Obama said.