Support for gay marriage among Americans has dipped slightly below 50 per cent, the Pew Research Center found in a survey released on Monday, even as bans on same-sex marriage have been ruled unconstitutional in a number of states this year.
The latest survey by Pew showed 49 per cent of Americans support same-sex marriage, down from 54 per cent when the organisation conducted a similar poll in February.
But it remains too early to tell if the drop off is the beginning of a more significant reversal in public attitudes on gay marriage or only an anomaly, Pew researchers said in a summary of their results.
The survey of 2,002 adults was conducted from Sept. 2-9 as part of a larger poll of Americans' view of religion in public life. It had a margin of error of plus or minus 2.5 percentage points.
The survey also found that 47 per cent of Americans believe wedding-related businesses, such as caterers and florists, should be allowed to refuse service to same-sex couples for religious reasons.
Americans' support for gay marriage has increased steadily in recent years, with the Gallup public research group in May finding support for gay marriage among Americans was at 55 per cent, a new high.
Nineteen states and the District of Columbia allow gay marriage.
Same-sex couples this year have scored a nearly unbroken string of victories in US courts, including a US 10th Circuit Court of Appeals decision striking down Utah's same-sex marriage ban and a similar ruling by the US Seventh Circuit Court of Appeals against bans by Indiana and Wisconsin.
Those decisions have been stayed pending appeals to the US Supreme Court.
More than 30 courts overall have ruled in favour of gay marriage since the Supreme Court in June 2013 struck down a key part of the 1996 federal Defence of Marriage Act, which denied benefits to same-sex married couples.