President Obama's stance opposing homosexual marriage, which he had described as "evolving," was a sore point for the country's gay and lesbian community, which helped elect him in 2008.

　　Mr. Obama has always supported efforts to ensure the same legal rights and civil liberties for gay couples as married straight couples.  But his opposition to same-sex marriage was thrust back to the spotlight after Vice President Joe Biden told NBC television's Meet the Press program on Sunday that he was "absolutely comfortable" with gay marriage.

　　Two other administration officials, including Mr. Obama's education secretary, also voiced their support for same-sex marriage.

　　In a hastily-arranged interview on Wednesday with ABC News, Mr. Obama said an "evolution" in his thinking led him to the decision, influenced by conversations with his staff, gay and lesbian members of the U.S. military and his family. "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," he said.

　　Mr. Obama pointed to his success in ending the "Don't Ask, Don't Tell" policy barring openly gay persons from serving in the military, and his opposition to the Defense of Marriage Act, which defines marriage as a union between a man and woman.  The president said he has always fought for the rights of gays and lesbians. "I have always been adamant that gay and lesbian Americans should be treated fairly and equally," he said.

　　Mr. Obama stressed that although his personal view on gay marriage has changed, he still supports the right of individual U.S. states to decide the marriage issue.

　　Analysts say the president's reversal probably will benefit his campaign for reelection against likely Republican Party nominee Mitt Romney.  Mr. Obama received substantial support from the nation's gay and lesbian community in 2008.

　　But the president and his campaign have had to gauge possible negatives of his new position, including the potential loss of support in relatively conservative states and among conservative ethnic minority voters.  In the political swing state of North Carolina, voters overwhelmingly approved a state constitutional ban on homosexual marriage on Tuesday.  Mr. Obama won North Carolina in 2008.

　　According to a recent Gallup public opinion survey, 50 percent of American believe that same-sex marriages should be recognized by law; 48 percent of those surveyed said such marriages should not be legal.

　　Mr. Obama is the first sitting president to explicitly support marriage for same-sex couples.  Organizations representing gay Americans and many political leaders have hailed his decision.

　　The chairman of the Republican National Committee, Reince Priebus, accused Mr. Obama of playing politics with gay marriage, saying that Republicans have not changed their position on the issue.