Abortion and gay marriage. For years, they've been lumped together as the paramount wedge issues of U.S. politics _ hot-button topics in the vortex of sexuality, personal freedom and public policy.

Yet these two divisive issues, prominent as ever this election season and still firing up the liberal and conservative bases of the two major parties, are evolving in intriguingly different ways. Partisans are taking care not to overstate how much the issues have in common.

Same-sex marriage vaulted into the spotlight when President Barack Obama declared his support this past week, and conservatives restated their opposition. Republicans deny Democrats' claims that they are waging a "war on women" that encompasses infringement of abortion rights.

Polls on same-sex marriage show a huge shift in public opinion in just a decade, from overwhelming opposition to a slight edge in favor. By contrast, attitudes toward abortion have scarcely budged over several decades, with a modest majority of Americans favoring some degree of abortion rights and opposition remaining both stable and vehement.

More profound is a moral difference. Americans who are ambivalent about same-sex marriage can decide to accept it with a live-and-let-live philosophy, while the abortion debate inherently involves hard questions about when life begins and whether a fetus has rights.

"Everybody knows gay people now _ their community left the ghetto a long time ago and is part of everyday life," said abortion-rights supporter Jon O'Brien of Catholics for Choice. "Abortion is very private, often a sad and difficult decision. It's entirely different."

Another difference: Acceptance of gays is now a given in popular culture, notably in the spate of hit TV shows such as "Glee" and "Modern Family" with gay and lesbian protagonists. There's no equivalent embrace of abortion rights in Hollywood's products; films depicting unintended pregnancies generally opt for a birth.

"It's harder to get out and advocate for abortion," said Tony Perkins, president of the conservative Family Research Council. "Hollywood and others have been more helpful to the gay and lesbian community in promoting them in their story lines."

Polls reflect divergent trends in how young adults _ Hollywood's favorite demographic _ view these two issues.

According to the Pew Research Center, Americans under 30 tilted slightly against same-sex marriage in 2004, and now favor it by 65 percent to 30 percent _ a higher approval rate than for older Americans.

"Assuming these trends continue, someone who supports same-sex marriage is probably heartened, because those most opposed are fading from the scene," said David Masci, a senior researcher with the Pew Forum on Religion and Public Life.

There's no equivalent shift or age gap on abortion. Pew's latest survey on the topic, in April, found that the views of young adults had been more or less stable in recent years and differed little from their elders. While 53 percent of those under 30 supported abortion rights, the approval rate was 55 percent among those aged 50 to 64.

One possible consequence: While same-sex marriage might be an issue that Democrats can use to energize youthful voters this year, that may be less likely with abortion rights.

"Abortion is an ongoing, protracted war," said O'Brien of Catholics for Choice. "Gay rights is the new kid on the block, the new thing, and it's doing particularly well."

Indeed, there's been concern among abortion-rights activists for a number of years that their cause doesn't galvanize large numbers of college students and other young adults.

Nancy Keenan, president of NARAL Pro-Choice America, cited the need for younger leadership in the movement as she announced Thursday that she'd be stepping down at the end of this year.

At the University of Wisconsin, political science professor Donald Downs says he's detected an upsurge of strength for local anti-abortion groups. "Even in Madison, I know social liberals who are uncomfortable with abortion," he said.

He also noted that the right to abortion has been established for four decades.

"It's not a huge issue unless it's taken away," Downs said. "With gay marriage, they're trying to establish it. It's a different psychology."

For the Republicans, both wedge issues present some strategic challenges.

In seeking conservative support during the primaries, presumptive GOP nominee Mitt Romney firmly pledged his opposition to gay marriage and abortion rights. Heading toward the general election, he must decide how hard to stress those stances as he woos the independent voters who will pick the winner.

A new AP-GfK poll of adult Americans showed Obama with a 21 percentage point lead over Romney on the question of who's most trusted to handle social issues such as abortion and same-sex marriage.

However, Dave Welch, a former Republican National Committee research director and campaign adviser to John McCain, predicted the marriage debate would play out in Romney's favor even if Obama gets a short-term benefit.

"Ohio, Florida, Indiana, North Carolina _ these are states Obama won by slim margins in 2008, and now the evangelicals there, who didn't come out for McCain, are galvanized," Welch said. "This could cost him the election."

As in recent election years, voters nationwide rate social issues _ including abortion and gay marriage _ as far less important than the economy or jobs. While 86 percent in a recent Pew poll said the economy would be very important to their vote for president, only 39 percent felt that about abortion and 28 percent in regard to gay marriage.

In the crucial swing state of Ohio, political scientist John Green of the University of Akron said it was difficult to forecast how the wedge issues might influence the outcome.

"They will not be the issues that will drive the election, but if it gets really close, they can make a difference," he said. "They bring a special set of voters to the polls who care very deeply."

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David Crary can be followed on Twitter at http://twitter.com/CraryAP