Obama's 'lipstick' reference
The US Democratic presidential candidate has denied claims of sexism after likening his rival's promise of change to putting "lipstick on a pig".
Barack Obama said Republican John McCain's outrage was "phoney", a diversion from debating real issues.
The controversy began on Tuesday after Mr Obama said his rival was advocating change while pursuing the politics of the current Bush administration.
Mr McCain's campaign accused him of smearing running mate Sarah Palin.
Mrs Palin joked last week that lipstick was all that separated a "hockey mom" and a pitbull.
Mr Obama made the remark during a rally in Virginia where he accused the McCain campaign of trying suddenly to adopt the promise of change - a platform he himself has been running on for months.
Drawing a link between the Republican senator for Arizona and President George W Bush, he suggested change would be impossible for Mr McCain to achieve.
"You can put lipstick on a pig. It's still a pig. You can wrap up an old fish in a piece of paper and call it change. It's still going to stink after eight years. We've had enough."
Mrs Palin, a self-described "hockey mom", made her joke about lipstick during a speech at the Republican National Convention last Wednesday.
Soon after Mr Obama's comments, McCain aides produced an election campaign ad referring to "sexism in American life", and accusing the Illinois senator of "smearing" Mrs Palin, governor of Alaska.
And there was speculation that Mr Obama might apologise, but he took a more aggressive line, says the BBC's Kevin Connolly in Washington.
He dismissed the "made-up controversy" on Wednesday - defending his remark as an "innocent expression".
Mr Obama said his comments had been taken out of context.
Republican advert attacks Obama
"The McCain campaign would much rather have the story about phoney and foolish diversions than about the future," the Illinois senator said.
Republicans may well try to keep the controversy going, although one difficulty for them is that John McCain has himself used the offending phrase, our Washington correspondent says.
Mr McCain had used the same analogy to criticise a health care plan presented by former Democratic presidential hopeful Hillary Clinton last year.
The row erupted as a new poll by the Wall Street Journal and NBC News suggested that Mr Obama and Mr McCain were in a statistical dead heat. Mr Obama held a lead of several points earlier this summer.
Another poll by CNN and the Opinion Research Foundation also put the rival candidates in a statistical tie, with Mr Obama polling 49% to Mr McCain's 48%.
The latest Gallup daily tracking poll of registered voters gave Mr McCain a lead of 49% to Mr Obama's 44%.