FARGO, N.D. - Sen. Barack Obama raised the possibility of slowing a promised gradual 16-month withdrawal from Iraq if he is elected president, saying Thursday that he would consult with military commanders on a coming trip to the region and "continue to refine" his proposals.

"My 16-month timeline, if you examine everything I've said, was always premised on making sure our troops were safe," Obama told reporters as his campaign plane landed in North Dakota, a state no Democratic presidential candidate has carried since 1964. "And my guiding approach continues to be that we've got to make sure that our troops are safe and that Iraq is stable. And I'm going to continue to gather information to find out whether those conditions still hold."

In a second, hastily convened news conference, Obama insisted that his policies had not changed and that he has "not equivocated" or "searched for maneuvering room" on Iraq. Consultations with commanders in the coming weeks would be focused more on the size of U.S. forces needed to train and equip Iraqi military and police units, as well as maintaining a "counterterrorism strike force" to prevent al-Qaida in Iraq from making a comeback, he said.

"Let me be as clear as I can be. I intend to end this war," he said. "My first day in office, I will bring the Joint Chiefs of Staff in, and I will give them a new mission. That is to end this war, responsibly, deliberately but decisively."

Thus far, he added, he has seen nothing to contradict his belief that one to two combat brigades could be pulled out each month over 16 months.

Obama, the presumptive Democratic nominee, has long said the nation "must be as careful getting out of Iraq as it was reckless going in." During his hard-fought primary fight with Sen. Hillary Rodham Clinton, he stuck to that 16-month timeline, building support for his candidacy among anti-war voters leery of the depth of Clinton's commitment to a pullout.

But since securing the nomination, a series of pronouncements has helped ease him toward the political center. He backed a compromise on warrantless wiretapping, criticized a Supreme Court decision preventing the death penalty for child rapists and failed to criticize another decision scuttling the District of Columbia's handgun ban.

Obama suggested that aides to his Republican rival, Sen. John McCain, had been working to create the impression "we were changing our policy when we haven't." And Republicans did not hesitate to pounce Thursday.

"There appears to be no issue that Barack Obama is not willing to reverse himself on for the sake of political expedience," said Republican National Committee spokesman Alex Conant. "Obama's Iraq problem undermines the central premise of his candidacy and shows him to be a typical politician."

The comments capped a shift in tone that has been occurring since June, and they fit with Obama's broader efforts to appeal to moderate and independent voters. Throughout the past week, Obama has been stressing values as he journeyed through conservative regions of swing states.