A CNN poll released Tuesday shows a narrow majority of Americans support giving gay and lesbian couples the right to marry.

Fifty-one percent of respondents said they support the legalization of gay marriage, while forty-seven percent disagreed, and two percent didn't know.

Tuesday's poll was the network's first to find opponents of gay marriage in the minority. In 2009, 54 percent of respondents said they opposed the institution.

Two previous national polls, one by the Associated Press and another by the Washington Post-ABC News, also concluded that a narrow majority of Americans favor legalizing marriage for gay couples.

As with previous surveys, the issue breaks down along political and geographic lines.

Sixty percent of Americans under 50 support gay marriage, but only 40 percent of respondents over 50 agree, the CNN poll found.

“More than six in 10 Democrats support same-sex marriage, joined by more than half of independents, but seven in 10 Republicans are against it,” CNN Polling Director Keating Holland said.

The poll comes as Republicans in the House pick up where the Obama administration left off in defending the Defense of Marriage Act (DOMA), the law that bans federal recognition of the marriages of gay and lesbian couples.