Obama's remarks nevertheless send a powerful signal, making him the first sitting U.S. President to come out in support of same-sex marriage.
In the interview, President Obama said he had always been adamant that gay and lesbian people should be treated fairly and equally, but, he added: "I had hesitated on gay marriage, in part because I thought civil unions would be sufficient … something that would give people hospital visitation rights and other elements we take for granted. And I was sensitive to the fact that for a lot of people the word marriage was something that evokes powerful traditions, religious beliefs, and so forth."
He changed his view after speaking to family and friends, including his own daughters. "I have to tell you that over the course of several years, as I talked to friends, and family and neighbors, when I think about members of my own staff who are incredibly committed, monogamous relations, same-sex relations, who are raising kids together, when I think of the soldiers, airmen, marines and sailors who out there fighting on my behalf and yet feel constrained even now though 'don't ask, don't tell' has gone, because they are not able to commit themselves in a marriage."
Representatives of gay organizations celebrated the long-desired announcement. Joe Solmonese, president of the Human rights Campaign, said: "His presidency has shown that our nation can move beyond its shameful history of discrimination and injustice. In him, millions of young Americans have seen that their futures will not be limited by what makes them different."
"In supporting marriage equality, President Obama extends that message of hope to a generation of young lesbian, gay, bisexual and transgender Americans, helping them understand that they too can be who they are and flourish as part of the American community."
There was caution and disappointment about President Obama's recent failure to pledge to issue an executive order on gay workplace rights.
"To be honest, it's a little frustrating," said Tiffani Bishop, a same-sex rights campaigner based in Austin, Texas, who has taken part in the Campaign for Southern Equality's bid to improve gay rights.
"Don't get me wrong, it's a great thing that he's come out in support finally. I'm very happy he's done that, but there are still some other things that he needs to really push hard on – one of them being the executive order."
Although same-sex marriages are recognized in some states, there remains widespread opposition, highlighted by an overwhelming vote in North Carolina on Tuesday night to reinforce a ban on gay and lesbian marriages.
Campaigners there welcomed President Obama's stance, but said they believed that even if his comments had come a day earlier they would not have influenced the result of the statewide ballot. Jeremy Kennedy of the Coalition to Protect NC families said: "We had a lot of endorsements on this including Bill Clinton. This really went beyond partisan politics. We had Republican supporters, Democrat supporters Democrats that weren't. Religion had a big part to play in the vote."
Jasmine Beach-Ferarra, of the Campaign for Southern Equality, said she was "heartened" to hear the president's support for gay marriage on a personal level.
"We understand his statement also says he believes the way to justice is on a state by state level. Our position as LGBT people in the south is that the path to equality is on a federal level, because we live as second class citizens in the southern states and people face daily discrimination."
President Obama acknowledged in the interview that he had been partly forced into making the decision early by the controversy over Vice President Biden's remark in a television interview on Sunday that he was comfortable with same-sex marriages.
Although polls show a consistent shift in public support in favor of gay rights, hostility remains strong among large portions of the electorate, including America's religious right.
Some Democratic strategists, including Obama advisers, proposed he leave the issue alone until after the White House election in November rather than risk alienating potential voters, especially in swing states such as North Carolina. Others argued that Obama, by sticking to his compromise position, looked weak and it was doing more damage than support of same-sex marriage.
The Obama administration ended Bill Clinton's messy "don't ask, don't tell" compromise policy on gay personnel in the military, but hesitated about taking the next step.
His Republican challenger, Mitt Romney, on Wednesday, responding to the controversy, expressed support for gay rights such as hospital visitation rights but he opposed same-sex marriage.
Ralph Reed, founder and chairman of Faith and Freedom Coalition, a conservative, anti-same-sex organization, condemned President Obama's shift as breaking a promise he made in 2008 to support traditional marriage.
"Combined with his administration's opposition to the Defense of Marriage Act, it reveals a president who is tone-deaf and out-of-touch with the time-honored values of millions of Americans. This is an unanticipated gift to the Romney campaign. It is certain to fuel a record turnout of voters of faith to the polls this November," said Reed.
Intellpuke: You can read this article by Guardian Washington, D.C., Bureau Chief Ewen MacAskill and Reporter Adam Gabbatt, in New York City, N.Y., in context here: http://www.guardian.co.uk/world/2012/may/09/barack-obama-supports-gay-marriage