Only 43 percent of those in the South back the referendum, while 62 percent of those in the East do.
The survey also found that the Supreme Court ruling striking down the Defense of Marriage Act earlier this month did little to change attitudes on same-sex marriage. The percentage of Americans saying that gay couples should have the ability to marry rose only a single percentage point from a similar survey in May.
"This adds to the body of evidence in Gallup trends that public opinion on gay marriage has reached a tipping point, whereby the majority now clearly supports it," said Gallup's Lydia Saad in a statement. "Nevertheless, the issue remains highly divisive, as large majorities of left-leaning, nonreligious, and younger Americans endorse it, while right-leaning, religious, and older Americans still oppose it."