WASHINGTON — Senator McCain is launching a new attack on a top Republican opponent, Mitt Romney, over inconsistencies in his stance on abortion.

The Arizona senator’s campaign sent out a missive to reporters alleging that the former Massachusetts governor was touting his defense of abortion rights six months after he said he had changed his mind on the issue. The e-mail contained a link to a YouTube video of Mr. Romney in May 2005 answering a question related to public funding of embryonic stem-cell research.

“I am absolutely committed to my promise to maintain the status quo with regards to laws relating to abortion and choice and so far I’ve been able to successfully do that,” he says in the video, “and my personal philosophical views about this issue is not something that I think would do anything other than distract from what I think is a more critical agenda.”

Mr. Romney, who had run for governor as essentially a “pro-choice” candidate, had announced his shift in position in November 2004. The McCain campaign used the clip to suggest that Mr. Romney had changed his stance only out of political convenience in advance of a presidential bid.

The Romney campaign hit back quickly and firmly, saying the quote was taken out of context and calling the McCain move the act of a “faltering and flailing campaign.”