WASHINGTON -- President Obama, marking the end of a prolonged “evolution” on the issue, now favors allowing homosexual couples to marry, he said in a television interview Wednesday.

The announcement comes days after Vice President Joe Biden’s comments that he was “absolutely comfortable” with gay marriage put new pressure on Obama to clarify his position on the issue.

Obama told ABC’s Robin Roberts Wednesday: “Over the course of several years as I have talked to friends and family and neighbors, when I think about members of my own staff who are in incredibly committed monogamous relationships, same-sex relationships, who are raising kids together, when I think about those soldiers or airmen or Marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that ‘don’t ask, don’t tell’ is gone, because they are not able to commit themselves in a marriage, at a certain point I’ve just concluded that for me personally, it is important for me to go ahead and affirm that I think same-sex couples should be able to get married.”

Obama’s new position realigns him with the growing number of Democratic officials who have embraced full marriage rights for gay and lesbian couples. Gay rights activists have widely believed that the president privately supported same-sex marriages, but withheld a public declaration out of concerns about alienating independent voters in key swing states.

There is a movement among activists in the party to adopt a so-called marriage equality plank in the official platform this summer. Such language would mark the continuance of the party’s own evolution. In 2000, the Democratic platform stated simply that the party supported “the full inclusion of gay and lesbian families in the life of the nation,” and “an equitable alignment of benefits.”

In 2004, in the face of an effort supported by the Bush campaign to put gay marriage bans to statewide referendums across the country, the Democratic platform stated that marriage “has been defined at the state level for 200 years, and we believe it should continue to be defined there.”

By 2008, the party vowed to “enact a comprehensive bipartisan employment non-discrimination act,” and opposed the Defense of Marriage Act “and all attempts to use this issue to divide us.”

It has been nearly a year and a half since Obama first indicated that his stance against gay marriage had begun to evolve. Obama has in fact taken multiple stances on the issue. In 1996, as a candidate for the state Senate in Illinois, he told a gay rights group that he favored same-sex marriages and would fight efforts to block them. As a candidate for U.S. Senate in 2004, Obama said he believed marriage is between a man and a woman, citing his faith as the underpinning reason for that belief.

In 2008, he repeated that assertion to influential evangelical pastor Rick Warren, adding “for me as a Christian it’s also a sacred union. God’s in the mix.” But Obama also said he would not support an amendment adding that definition to the Constitution.

Defining marriage “has been a matter of state law. That has been our tradition,” he said. At the same time, Obama opposed a California ballot initiative outlawing same-sex marriage because it was “divisive and discriminatory.”

Obama had plenty of company in such murky waters. All of his top competitors for his party’s nomination drew the same line -- opposing marriage and arguing that civil unions were sufficient to protect the legal rights of gay couples.

Since then, Obama’s party has steadily drifted away from that position -- and the president tried to suggest, without stating clearly, that he’s moving with it. In October 2010, during a question-and-answer session with progressive bloggers, Obama first signaled he was reconsidering his previous position.

“I am a strong supporter of civil unions. As you say, I have been to this point unwilling to sign on to same-sex marriage primarily because of my understandings of the traditional definitions of marriage,” he told Joe Sudbay of AmericaBlog. “But I also think you’re right that attitudes evolve, including mine. And I think that it is an issue that I wrestle with and think about because I have a whole host of friends who are in gay partnerships. I have staff members who are in committed, monogamous relationships, who are raising children, who are wonderful parents.”

At a news conference nearly two months later, after he signed a repeal of the “don’t ask, don’t tell” policy, Obama restated his “baseline” position, support for “a strong civil union that provides them the protections and the legal rights that married couples have.”

“I think that’s the right thing to do. But I recognize that from their perspective it is not enough, and I think is something that we’re going to continue to debate and I personally am going to continue to wrestle with going forward,” he said.

The president’s stated “evolution” was widely viewed as a wink and a nod to gay rights activists. Still, the president’s advisors gave no indication that they planned to come out with a new stance before the November election.

Biden’s comments appeared to shift that calculus. While the White House claimed the remarks were essentially a restatement of the president’s position, it was obvious they were everything the president’s stance was not: open and clear.

As the issue snowballed, Biden’s comments demonstrated how difficult Obama’s “evolution” would be to explain in a debate -- as the president will undoubtedly be asked to do -- or even in a media briefing, as White House spokesman Jay Carney experienced in a spirited media briefing filled with elliptical or incomplete answers.

On Monday, Republican National Committee chairman said the episode exposed an authenticity problem for the president. Publicly at least, Obama shared the same position as Mitt Romney, that marriage should be between one man and one woman.

“He doesn’t want to fully embrace what his vice president is saying, but he wants the benefit of what the vice president is saying,” he told MSNBC. “People just aren’t buying what he’s selling because they don’t believe he’s real anymore, that it’s politics. And he has become the ultimate Washington politician, and this latest episode in regard to gay marriage is a great example of that.”

michael.memoli@latimes.com

kathleen.hennessey@latimes.com