U.S. President Barack Obama has declared unequivocal support for gay marriage, becoming the first president to endorse the politically explosive idea and injecting a polarizing issue into the 2012 race for the White House.

Obama's announcement, after refusing to take a clear stand for months, cheered gay rights groups who have long urged him to support gay marriage. It also opened up a distinct area of disagreement with Republican presidential candidate Mitt Romney, who opposes gay marriage.

Polling suggests the nation is evenly divided on the issue.

"I have hesitated on gay marriage in part because I thought that civil unions would be sufficient," Obama said on Wednesday in an interview with ABC at the White House. He added that, "I was sensitive to the fact that for a lot of people the word 'marriage' was something that invokes very powerful traditions, religious beliefs and so forth."

Now, he said, "it is important for me personally to go ahead and affirm that same-sex couples should be able to get married."

Same-sex issues

The president's decision to address the issue came on the heels of a pair of events that underscored the sensitivity of the issue.

U.S. Vice-President Joe Biden said in an interview on Sunday that he is completely comfortable with gays marrying, a pronouncement that instantly raised the profile of the issue. And on Tuesday, voters in North Carolina — a potential battleground in the fall election — approved an amendment to the state constitution affirming that marriage may only be a union of a man and a woman.

The president has already supported a number of initiatives backed by gays, including an end to the military's "don't ask, don't tell" policy, and a decision not to defend in court a federal law that was designed as an alternative to gay marriage.

He had stopped short of supporting gay marriage, though, saying his position was "evolving."

Making it personal

Obama spoke about his support for gay marriage in deeply personal terms, saying his young daughters, Malia and Sasha, have friends whose parents are same-sex couples.

"Malia and Sasha, it wouldn't dawn on them that somehow their friends' parents would be treated different," Obama said. "It doesn't make sense to them and frankly, that's the kind of thing that prompts a change in perspective."

Obama said his wife Michelle Obama also was involved in his decision and joins him in supporting gay marriage.

"In the end the values that I care most deeply about and she cares most deeply about is how we treat other people," he said.

Acknowledging that his support for same-sex marriage may rankle religious conservatives, Obama said he thinks about his faith in part through the prism of the Golden Rule — treating others the way you would want to be treated.

"That's what we try to impart to our kids and that's what motivates me as president, and I figure the most consistent I can be in being true to those precepts, the better I'll be as a dad and a husband and hopefully the better I'll be as president," Obama said.

Tricky politics

The political cross-currents are tricky.

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 governor Ed Rendell, a Democrat, told Obama to "man up" and take a position on gay marriage.

Romney has not generally raised the issue in his campaign.

On Wednesday, he told KDVR-TV in Denver that "I do not favour marriage between people of the same gender, and I do not favour 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."