Max Whittaker, Getty Images
Republican U.S. vice presidential candidate and Alaska Gov. Sarah Palin greets her supporters at a campaign rally on Saturday.

For evidence of how intensely the presidential candidates are battling over women, consider their investment in Oprah Winfrey. After the news programs, "Oprah" is the chief recipient of campaign advertisements this year, with Sen. John McCain buying more commercial spots on the program in the last month than Sen. Barack Obama — even though Winfrey herself is backing Obama.

Obama, the Democratic presidential nominee, is teaming stars from soap operas and "Sex and the City" with congresswomen in contested states. McCain, the Republican nominee, is sending tailored mailings on taxes to women who drive minivans, watch "The Biggest Loser" or "Lost" and know their way to the nearest big-box store.

And both campaigns are trying to highlight the issues they think will draw more support from women, with Obama emphasizing pay equity and abortion rights and McCain playing up his "maverick" image and raising questions of respect for his running mate, Gov. Sarah Palin of Alaska.

The fierce, and complicated, competition for the female vote has been escalated by McCain's vice presidential selection. Even before Palin joined the ticket, Obama was moving to shore up support from women, especially those who had supported Sen. Hillary Rodham Clinton in the Democratic primaries.

Now Obama campaign officials are stepping up their efforts, and both campaigns are recalibrating pitches to women to navigate cultural forces and policy positions that can give them an advantage.

In particular, they are competing for working-class white women, the group that could be especially pivotal in the states likely to decide the election.

For Obama, the push for women means emphasizing that he is running against McCain, not Palin, and drawing attention to McCain's record on issues that particularly resonate with women: his opposition to abortion rights, his votes against expanded health insurance for children and pay equity legislation, and his support for private investment accounts for Social Security, of concern among white women over 50, a group Obama has had trouble winning over.

This week, Obama events have a theme, "Women for the Change We Need," as the campaign tries to connect with women in conference calls, rallies and registration drives.

The campaign will also begin increasing advertising on television programs watched by women — besides "Oprah," some of the biggest investments for the campaigns have been during "Dr. Phil," "Live With Regis and Kelly" and "The Ellen DeGeneres Show."

Each campaigns is also beginning to put more spots on Lifetime, and a McCain media buyer recently lamented that the Food Network did not accept political advertising.

McCain will continue to campaign this week with Palin, with a rally on Tuesday in Ohio, an important state for working-class women. The two are expected to be together frequently in the seven remaining weeks of the campaign.

Beyond that, the McCain campaign's strategy is to emphasize personality, capitalizing on the booming celebrity of Palin, highlighting McCain's story as a war hero, showcasing their families, and trying to keep alive the anger about sexism that many women felt during Obama's primary campaign against Clinton. Democrats have relied heavily on women in recent presidential elections — so much so that McCain strategists say they believe that to win they need to run even among women overall, and lead among white women.

Women have voted in greater proportions than men for almost three decades — in 2004, nearly 9 million more women voted than men, 67.3 million to 58.5 million. But the hard-fought candidacy of Clinton and McCain's selection of Palin as the first woman on a Republican presidential ticket have put new cultural and ideological elements more fully into play.

"It's because there were these women who supported Hillary Clinton, some of whom so visibly said they might not support Obama or might sit it out or vote for John McCain," said Susan Carroll, a senior scholar at the Center for American Women and Politics at Rutgers who has written extensively on the gender gap in voting. "That really called attention to the fact that women were going to be critically important."

McCain's strategists do not expect to win more than a small fraction of Clinton's supporters. But they do see blocs of women they think they can win.

Democrats have been accused of taking women for granted, in part because they have been able to count on them: More women have voted Democratic in the last four presidential cycles. More men have voted Republican in all but two of the last nine, the exceptions being 1976, when Jimmy Carter was the Democratic candidate, and 1992, when Bill Clinton was elected.

But white women have voted Republican in all but two of the last nine presidential elections. In 1992, they were evenly divided between the first President Bush and Bill Clinton; in 1996, they voted for Clinton, 48 percent to 43 percent. And while unmarried women have consistently given their majority to Democrats, married women gave President Bush the majority in 2004.

"It's about how much Democrats can maximize the gender difference and how much the Republicans can hold it down," Carroll said.

The McCain campaign's polling identifies two ripe demographics: So-called Wal-Mart women, who shop at the store at least once a week, earn less than $60,000 a year, have less than a college education, and hold a poor impression of Bush; they tend to call themselves independents and say their economic situation is fair or poor, listing the economy as their prime election issue. McCain strategists believe this group will be attracted by the ticket's "maverick" image.

The second group is women in important suburbs in Florida, Michigan, Missouri, Pennsylvania and Wisconsin.

The McCain campaign is also on the offensive in trying to stoke anger about perceived sexism. The campaign has designated a squad of prominent Republican women to call out what they see as gender-based smears against Palin. Last week, it released two spots accusing Obama of being "disrespectful" toward her.

Obama appears to have a strong advantage among young, unmarried women. But, said Anita Dunn, a senior adviser: "We are not ceding women with children. We have a candidate whose wife is a working mom with two young children."

In part, the Obama campaign is emphasizing the Republican ticket's opposition to abortion rights. The campaign ran a radio advertisement during the Republican convention calling the party's platform on abortion "extreme" because it did not include an exception for rape or incest.

But that issue alone may not swing many women. In a Gallup poll in May, 14 percent of women said that a candidate for major office must share their view on abortion (about the same percentage as among men). For half the women in the poll, abortion was one issue among many affecting their decision.

The Obama campaign is also emphasizing McCain's opposition to pay equity legislation, with a television spot that began running on Sunday saying that he "just doesn't get it."

The Obama campaign's focus on women this week will start with a conference call Wednesday between 20,000 women in leadership positions nationwide and Obama's running mate, Sen. Joseph R. Biden Jr. of Delaware, who the campaign believes commands respect among women, particularly because of his advocacy for laws against domestic violence. Biden and Obama will then hold rallies with women Thursday and Friday, setting up a weekend of voter registration, beauty shop canvassing and mobilizing events.

To secure working-class women, the campaign sees Hillary Clinton as its best surrogate, and has sent her to Florida, Nevada and Ohio, states she won in the primaries. In recent days, female aides and surrogates to Obama have also begun arguing in television appearances that McCain has a history of insensitivity toward women — recalling a joke he made about Chelsea Clinton's appearance when she was a teenager, or his going along at a South Carolina event last year when a woman used a coarse term to refer to Clinton. (McCain now frequently lauds Clinton.)

Though there is little question that Palin's bursting onto the scene has put pressure on the Obama campaign, it is unclear how much difference she will make. Geraldine A. Ferraro created a small bounce in the polls when Walter F. Mondale chose her as his running mate in 1984, making her the first woman on a major party ticket. But in the end, the nation went in a landslide for President Ronald Reagan.

"Ultimately in that election," Carroll said, "people voted the top of the ticket."