"Gov. Romney is for an amendment to the U.S. Constitution that would enshrine discrimination into our founding legal document," Carney said. "The president thinks that's wrong. So their positions were starkly different before yesterday."
Romney, and Republican leaders in Congress tried, for their part, to steer the focus of the presidential campaign back to the nation's sluggish economy.
In Seattle, where he was attending two fund-raisers, Obama witnessed the support firsthand as his motorcade passed a woman holding an infant and a sign that said: "Thank you! Mr. President for standing up for my mommys!"
He drew big cheers from supporters at Seattle's historic Paramount Theater when he said his vision for a better America applies to everyone, "no matter what you look like, no matter what your last name, no matter who you love."
Without referring directly to marriage, Obama expanded on the theme of same-sex equality.
"We are moving forward to a country where every American is treated with dignity and with respect and here in Washington you'll have the chance to make your voice heard on the issue of making sure that everybody, regardless of sexual orientation, is treated fairly," Obama said. "You'll have a chance to weigh in on this. We are a nation that treats people fairly."
Washington state has passed a law approving same-sex marriage, but opponents there are gathering signatures for a ballot initiative to overturn the law and declare marriage as a union of man and woman.
Outside the Paramount, Teri McClain, 44, was holding a double-sided sign expressing gratitude to the president for "evolving on same-sex marriage."
"He's looking out for the good of the people, and this is what the people want," McClain said.
Though the timing of his announcement was not of Obama's choosing, the campaign was not shying away from the issue even though aides conceded it held some political risk for the president. Just hours after Obama voiced his support for gay marriage in an ABC interview, the campaign e-mailed a clip of the interview and a personal statement from the president to its vast list of supporters, drawing attention to his stance.
Still, Obama said Vice President Biden got "a little bit over his skis" in publicly embracing gay marriage, forcing Obama to speed up his own plans to announce support for the right of same-sex couples to marry.
"Would I have preferred to have done this in my own way, in my own terms, without, I think, there being a lot of notice to everybody? Sure," Obama said. "But all's well that ends well."
Biden apologized to Obama on Wednesday for getting ahead of him, a person familiar with the exchange said. The person, who spoke on condition of anonymity to describe the private discussion, said Obama accepted the apology and told Biden he knew Biden's own words of support for gay marriage were heartfelt.
Hollywood has been outspoken in its support of gay rights.
Clooney's dinner was organized by Jeffrey Katzenberg, the CEO of DreamWorks Animation, and was to include such celebrity guests as Robert Downey Jr. and Barbra Streisand. The event was initially to be a spring gala hosted by Katzenberg at his house. But Katzenberg's home is under renovation, so Clooney offered to host instead.
That prompted the Obama campaign to conceive an online raffle for the general public. Tens of thousands of people participated, drawn by the campaign's pitch: "For a chance to hang out with President Obama at George Clooney's house, donate $3 or whatever you can to be automatically entered to win."
As a result, nearly two-thirds of the money raised for the event will be from people who won't attend. The two winners were Beth Topinka of Manalapan, N.J., and Karen Blutcher of St. Augustine, Fla.
Obama doesn't have the power to make same-sex marriage legal. But his announcement had long been sought by gay-rights advocates, who cheered his public affirmation of gay marriage.
Romney quickly reiterated his opposition to same-sex marriage. "I believe that marriage is between a man and a woman," he said Wednesday in Oklahoma.
On Capitol Hill, House Speaker John A. Boehner (Ro., Ohio) deflected questions about same-sex marriage, declaring: "The president can talk about it all he wants. I'm going to stay focused on what the American people want us to focus on, and that's jobs."
This article contains information from the New York Times News Service.