A poll of 1,001 American voters has found that almost half believe being gay is something people choose.
The research found that 47 per cent of respondents thought homosexuality was a choice, while 46 per cent opposed gay marriage.
It was carried out by polling institute Angus-Reid.
Fifty-three per cent of respondents in this poll approved of the measure, while 37 per cent were opposed and ten per cent were undecided.
Marriage was more contentious, with 46 per cent opposed to full equality. Forty-three per cent were in favour while one per cent were unsure.
The respondents who were most in favour of gay marriage tended to be cohabiting, single or widowed people.
Married, separated and divorced people were less in favour.
The poll also asked whether respondents had close friends or relatives who were gay. Fifty-three per cent said they said, 46 per cent said no and two per cent would not answer.
On whether people chose to be gay, 34 per cent said it was something people were born with. Twenty per cent said they did not know.
The poll surveyed American adults on December 9th and 9th. It has a margin of error of plus or minus 3.1 percent.
Connecticut, Massachusetts, New Hampshire, Iowa and Vermont give gay couples the right to marry.
The right was withdrawn in California last year and a bill failed in New York last week. Voters repealed the right in Maine last month.
Washington DC will legalise gay marriage early next year if Congress approves its bill.
Thirty US states have explicit constitutional bans on recognising gay marriage.