Sixty-eight percent of respondents to the poll said they did not think marriage between homosexuals should be recognized by law and given the same rights as traditional marriages.
The poll also found nearly three out of five respondents said they would support an amendment barring same-sex marriage, an increase since a poll in November.
Just over a quarter -- 27 percent -- of respondents said they would support civil unions for gay couples, while 45 percent said neither civil unions nor same-sex marriages should be legal.
The survey's results were based on telephone interviews conducted March 18-20 with 909 U.S. adults, with sub-samples of 443 and 466 respondents. The margin of error ranges from 4 percentage points to 5 percentage points.