(Adds Republican response, paragraph 7)
By John Whitesides, Political Correspondent
ST. LOUIS, July 5 (Reuters) - Democratic presidential candidate Barack Obama said on Saturday his plan to end the Iraq war was unchanged and he was puzzled by the sharp reaction to his statement this week that he might "refine" his timetable for withdrawing U.S. combat troops.
"For me to say that I'm going to refine my policies I don't think in any way is inconsistent with prior statements and doesn't change my strategic view that this war has to end and that I'm going to end it as president," Obama told reporters on his campaign plane.
Obama, who based his drive to capture the Democratic nomination on his early and ardent opposition to the war, said earlier this week he might alter his plan to bring combat troops home within 16 months of taking office if conditions on the ground changed.
The comment drew heavy coverage and sharp criticism from some on the left and the right, with Republicans saying it showed he was vacillating on Iraq.
"I was a little puzzled by the frenzy that I set off with what I thought was a pretty innocuous statement," he said on a flight from Montana to St. Louis. "I am absolutely committed to ending the war. I will call my joint chiefs of staff in and give them a new assignment and that is to end the war."
Obama will face Republican John McCain, a staunch advocate of the war, in a November presidential race that is certain to focus heavily on the future of U.S. troops in Iraq.
"What's really puzzling is that Barack Obama still doesn't understand that his words matter," said McCain spokesman Tucker Bounds.
Obama said he did not make a mistake with his earlier choice of words in describing his Iraq position -- even though he called a second news conference a few hours after his initial comments to clarify his stance.
He laid the blame with reporters.
"I'm surprised at how finely calibrated every single word was measured. I wasn't saying anything I hadn't said before, that I didn't say a year ago or when I was a United States senator," said Obama, who is still a senator from Illinois.
"If you look at our position, it's been very consistent," he said. "I am unwavering in the belief that this has been a strategic mistake and that this war has to end. It would be a further strategic mistake for us to continue with an open-ended occupation of the sort that John McCain has promised."
Obama said his willingness to consider changing conditions on the ground and the potential ramifications of the pull-out plan was a strength -- and a sharp contrast to Republican President George W. Bush's stay-the-course strategy in Iraq.
"The tactics of how we ensure our troops are safe as we pull out, how we execute the withdrawal -- those are things that are all based on facts and conditions," he said.
"I'm not somebody who, like George Bush, is willing to ignore facts on the basis of my preconceived notions. I want to pay attention to what is happening on the ground."
Under heavy pressure from McCain, who criticized his failure to visit Iraq since 2006, Obama plans to travel to Iraq and Afghanistan. The dates have not been announced for security reasons but the trip is expected within the next month.
While Obama would not admit a mistake in describing his views on Iraq, he said he had plenty of room for improvement as a presidential candidate.
"One of the things I've always tried to do is learn from mistakes and try to get better," he said.
"There is a learning curve and growth being a presidential candidate. I think I'm a much better candidate now than I was six months ago or 12 months ago. I think I'll be a better communicator and even more effective six months from now." (Editing by John O'Callaghan) (For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)