Another American poll suggests that just over half of voters support marriage equality.
The CNN poll found that 51 per cent of the 824 adults surveyed said gay couples should be allowed to wed.
Among those under 50, support levels rose to 60 per cent.
CNN polls in 2008 and 2009 found that just 44 per cent of those surveyed supported gay marriage.
Women showed substantially higher levels of support in the latest poll. Fifty-seven per cent said gay marriage should be legal, compared to just 45 per cent of men.
Only 27 per cent of Republicans agreed with gay marriage. Sixty-four per cent of Democrats were in support.
The wording of the question was: “Do you think marriages between gay and lesbian couples should or should not be recognised by the law as valid, with the same rights as traditional marriages?”
In March, a Washington Post-ABC News poll of 1,001 people found that 53 per cent supported gay marriage.
Five states – Massachusetts, Connecticut, Iowa, New Hampshire and Vermont – and the District of Columbia – currently allow gay couples to marry.
California’s ban is under review. Maryland was expected to be next to make the change but a bill failed to gain the necessary support.
In the US, the Defense of Marriage Act bars the federal government from recognising gay marriage. The Obama administration recently announced it would no longer defend the law in court, although the Republican-controlled House has appointed a lawyer to do so.