Obama says he has concluded that it is important for him to affirm that he thinks same-sex couples should be able to get married. He says he came to the conclusion over the course of several years of talking to family and friends.
Obama has previously said his personal views of gay marriage were evolving, a stance that frustrated gay rights supporters.
Obama revealed his support for gay marriage in an interview with ABC News.
THIS IS A BREAKING NEWS UPDATE. AP's earlier story is below.
WASHINGTON (AP) - President Barack Obama faced mounting pressure Wednesday to express support for same-sex marriage after a setback for gay-rights advocates in North Carolina.
Republicans there turned out in force Tuesday night to vote to strengthen the state's gay marriage ban. The passage of the state constitutional amendment, by a whopping 61 percent of the vote, proves that the topic remains a powerful election-year wedge issue despite tough economic times. It also illustrates the risks for the president as Democrats press him to do what no other has before: back gay marriage.
The vote - in a state that Obama won in 2008 and that will host his nominating convention in September - came just days after Vice President Joe Biden and Education Secretary Arne Duncan voiced their support for gay marriage in back-to-back television interviews, comments the White House insisted were not intended to pave the way for Obama to embrace gay marriage.
Yet, Obama appeared ready to add his voice to this week's debate in a Wednesday afternoon interview with ABC News that the White House hastily arranged. He was expected to be pressed in the interview on his views on gay marriage.
White House officials would not say whether the president planned to announce a shift in his position.
Obama backs many gay rights; he does not support gay marriage but says his personal views are evolving.
In recent days, the issue has started to roil the presidential race. The White House has been inundated with questions about the president's position. And GOP rival Mitt Romney - who has an inconsistent record on gay rights but long has been opposed to same-sex marriage - trying to sidestep the matter at a time when most Americans say they support gay unions.
By Wednesday, the president found himself caught between two schools of thought among his backers.
Some top aides argued that gay marriage is toxic at the ballot box in battleground states like North Carolina and Virginia because, as Tuesday's vote proved, the issue remains a reliable way to fire up rank-and-file Republicans. It also could open Obama up to Republican criticism that he was taking his eye off the economy, voters' No. 1 issue.
Other Democratic supporters claim Obama could energize huge swaths of the party, including young people, by voicing his support for gay marriage before November. He also could appeal to independent voters, many of whom back gay marriage, and he could create an area of clear contrast between himself and his Republican rival as he argues that he's delivered on the change he promised four years ago.
On Tuesday, former Pennsylvania Gov. Ed Rendell, a Democrat, told Obama to "man up" and take a position on gay marriage.
If Obama doesn't do so soon, the calls for him to do so likely will only grow. Obama is scheduled to headline two high-dollar fundraisers for gay and lesbian supporters, including one in New York on Monday. And several prominent Democrats, including his campaign co-chair Caroline Kennedy, are pushing for support for gay marriage to be included in the party platform that will be ratified when Obama accepts the Democratic nomination.
For Romney and the Republicans, the topic comes with both benefits and drawbacks given that polls show that a slim majority of the country - and an increasing number of independent voters - now support same-sex unions.
Romney was treading carefully as the hot-button issue re-emerged in the campaign. He favors a constitutional amendment to ban gay marriage, saying the policy should be set federally, not by states. But some conservatives question Romney's record on gay rights issues and point to his assertion in a 1994 Senate campaign that he supports "full equality" for gays and lesbians.
On Wednesday, he told KDVR-TV in Denver that "I do not favor marriage between people of the same gender, and I do not favor civil unions if they are identical to marriage other than by name. My view is the domestic partnership benefits, hospital visitation rights, and the like are appropriate but that the others are not."
The Romney campaign did not respond to questions about which benefits the Republican candidate would oppose.
The former Massachusetts governor told an Ohio television station Monday that he believes "marriage is between a man and a woman, and that's a position I've had for some time and I don't intend to make any adjustments at this point - or ever, by the way."
Public opinion on gay marriage has shifted in recent years, with most polls now finding the public tilting in favor of legal same-sex marriages.
A Gallup poll released this week found 50 percent of all adults in favor of legal recognition of same-sex marriages, marking the second time that poll has found support for legal gay marriage at 50 percent or higher. Majorities of Democrats (65 percent) and independents (57 percent) supported such recognition, while most Republicans (74 percent) said same sex marriages should not be legal.
Six states - all in the Northeast except Iowa - and the District of Columbia allow same sex marriages. In addition, two other states have laws that are not yet in effect and may be subject to referendums.
Yet, illustrating how politically tricky the issue is, North Carolina on Tuesday became the 30th state to pass a constitutional amendment banning gay marriage.
Both the Obama and Romney campaigns were watching the North Carolina vote closely. North Carolina is considered the most politically moderate and progressive state in the South, and voters there narrowly sided with Obama in the 2008 presidential election.
Yet the state is still deeply conservative on social issues. Church leaders rallied their congregations to vote for the amendment and the Rev. Billy Graham, who at age 93 remains influential even though his last crusade was in 2005, was featured in full-page newspaper ads supporting the measure.
North Carolina law already bans gay marriage, but an amendment effectively seals the door on same-sex marriages. The amendment also goes beyond state law by voiding other types of domestic unions from carrying legal status, which opponents warn could disrupt protection orders for unmarried couples.
Obama weighed in early with his opposition to the North Carolina amendment. Aides insisted there was no conflict between the president opposing a measure that banned gay marriage and not publically supporting gay marriage itself. A spokesman said Tuesday night that the campaign was "disappointed" in the outcome.
North Carolina is an important piece of the electoral puzzle for the Obama campaign in November election, but the president could still win the White House again without it.
AP Deputy Director of Polling Jennifer Agiesta and Philip Elliott in Colorado contributed to this report.