St. Paul, Minnesota. - Barack Obama has launched a broadside against John McCain's opposition to abortion rights and moved one of the most divisive issues in modern American politics to the airwaves on a large scale for the first time in this presidential campaign.

    Obama's new radio ad, airing widely in at least seven swing states, tells voters McCain "will make abortion illegal." It's airing as McCain courts female voters with the addition of the staunchly anti-abortion governor of Alaska, Sarah Palin, to his ticket.

    Democrats had, until now, sought to appeal to women primarily on economic issues such as health care and workplace discrimination; abortion rights were hardly mentioned at the Democratic National Convention in Denver last week. But women's rights groups have been urging Obama to attack McCain on the issue, pointing to polling showing that some women who support McCain think he supports abortion rights. In fact, the Arizona senator has long supported a ban on abortions, with exceptions for victims of rape and incest, and for pregnancies that threaten the life of the mother. Palin has an even firmer anti-abortion stance: She would require rape and incest victims to carry their pregnancies to term.

    "Let me tell you: If Roe vs. Wade is overturned, the lives and health of women will be put at risk. That's why this election is so important," says the nurse-practitioner who narrates Obama's ad. "John McCain's out of touch with women today. McCain wants to take away our right to choose. That's what women need to understand. That's how high the stakes are."

    An announcer then claims that "as president, John McCain will make abortion illegal," before playing an exchange on "Meet the Press" in which McCain told moderator Tim Russert that he favors "a constitutional amendment to ban all abortions."

    "We can't let John McCain take away our right to choose. We can't let him take us back," says the ad.

    Obama supports abortion rights, though he was criticized by Sen. Hillary Rodham Clinton in the Democratic primary for avoiding votes on controversial abortion issues.

    Obama spokesman Bill Burton said the ad about McCain was sent to stations last Thursday, before the choice of Palin was made public.

    "This is a straightforward ad about the very well-documented fact that he wants to overturn Roe v. Wade and supports a constitutional ban on abortions," said Burton.

    The campaign didn't release further details of the ad buy, but Politico readers reported that it's airing in Florida, Virginia, Iowa, Ohio, Indiana, Wisconsin and Colorado.

    One Colorado reader said he'd heard it about a dozen times Tuesday - signs of a large buy.

    McCain aides didn't respond to a question about the ad, but Republican Party communications director Danny Diaz responded by attacking Obama's opposition to an Illinois bill that advocates said would protect babies who survived abortions, and critics said was an attempt to limit all abortions.

    "Barack Obama voted against a bill that would have protected infants born alive having survived an abortion attempt," said Diaz. "He has offered misleading statements on the issue and is now trying to confuse voters by attacking Senator McCain."

    Kate Michelman, an informal Obama adviser who is the former president of the abortion-rights group NARAL Pro-Choice America, said she expected the campaign to expand its appeal to women on issues of abortion rights.

    "This is a door opened to a longer campaign and strategic effort to ensure that women know the truth about John McCain and Gov. Palin," she said, suggesting it would come "on the radio, in the mail, on the phones, and in the organizing on the ground."

    Though the campaign says the ad was released before Palin was chosen, Michelman said her selection, and her strong anti-abortion stance, would drive the issue closer to the center of the race.

    "By his nomination of Gov. Palin, McCain has made his opposition to a woman's right to decide a major campaign issue," she said.