Democratic presidential hopeful Barack Obama rejected charges on Tuesday that he has shifted positions on Iraq and other issues as part of a move to the political centre now that he is his party's nominee.

As he positions himself for the battle against Republican John McCain, the Illinois senator softened an earlier vow to reopen the North American Free Trade Agreement, did not oppose a Supreme Court decision striking down Washington's gun ban and said he would support expanding the government's wiretap authority.

Most recently, he signalled greater flexibility on his pledge to quickly pull U.S. troops out of Iraq, telling reporters last week he might "refine" his views based on what happens on the ground.

Asked about his Iraq policy at a town hall meeting in Powder Springs, Obama rejected claims he was softening his insistence on a withdrawal of U.S. troops from the country.

He also said he hoped he could more generally counter "this whole notion that I am shifting to the centre or that I'm flip-flopping or this or that."

"You know, the people who say this apparently haven't been listening to me," Obama said.

The McCain campaign has eagerly accused Obama of shifting position for political expediency - a tactic Republican President George W. Bush used successfully in his 2004 re-election campaign against Democrat John Kerry.

"I think there's been definitely shifts in position, and one of them is Iraq," McCain told the Fox News Channel on Tuesday.

Obama, who has a single-digit lead over McCain in the polls heading toward the November election, has also been criticized by some liberal supporters, particularly over his support for electronic eavesdropping legislation.

Pundits believe he is attempting to position himself closer to the centre in hopes of winning over independent voters, moderate Democrats and some Republican voters who have grown disenchanted with Bush.

'LURCHING' TO THE RIGHT?

In an opinion piece in Tuesday's New York Times, columnist Bob Herbert accused Obama of "lurching" away from liberal positions. "Senator Obama is not just tacking gently toward the centre," Herbert said. "He's lurching right when it suits him, and he's zigging with the kind of reckless abandon that's guaranteed to cause disillusion, if not whiplash."

But Obama said he wanted his supporters to know that although he might not agree with each of them on every issue, when he differs it is not because he is playing politics.

"One of the things that you find as you go through this campaign is that everybody became so cynical about politics that the assumption is that you must be doing everything for political reasons," he said. "Don't assume that because I don't agree with you on something that it must be because I'm doing that politically."

Later, Obama, addressing Latino voters, accused McCain of abandoning his position on immigration reform. "We need a president who isn't going to walk away from something as important as comprehensive reform when it becomes politically unpopular," he told the League of United Latin American Citizens.

McCain broke with his Republican party and worked for a plan to offer a path to citizenship for illegal immigrants. But the immigration plan failed in Congress. Obama has faulted McCain for shifting during the fight for his party's nomination to an emphasis on the need to secure the U.S. borders before addressing the status of illegal immigrants.

Speaking to the same Latino group earlier, McCain, who believes he has a chance to win over some Hispanic voters who have traditionally been a part of the Democratic base, emphasized his economic proposals. McCain said his tax policies would help fuel small-business growth.

"Small businesses are the job engine of America, and I will make it easier for them to grow and create more jobs," the Arizona senator said. On immigration, McCain noted he worked with Senate colleagues twice to try to craft broad reform.