The changes echo times when attitudes toward African-Americans and women were in flux, scholars say. With young adults by far the most tolerant of homosexuality among those 18 to 29 years old, 73 percent support same-sex marriage the trend seems more likely to accelerate than reverse.
More than a third of Americans surveyed say their views have changed significantly over time toward gay marriage, an issue being battled in states across the country and before the U.S. Supreme Court. The high court could announce soon whether it will accept cases challenging California's Proposition 8 and the 1996 Defense of Marriage Act, which bars federal programs from recognizing same-sex marriages.
"They have changed from 'this is appalling' to, you know, 'what is wrong with that idea?' " said Mary Ann Schmertz, 82, a real estate agent in Wilkinsburg, Pa., describing her own views on the issue. In a follow-up interview after she was polled, she noted that her next-door neighbors are a gay couple.
"Why should they be discriminated against?" she said. "They're paying taxes. They're leading decent lives."
To be sure, significant opposition remains. While 53 percent support gay marriage, 46 percent oppose it. A third would go further: They say gay or lesbian relations between consenting adults should be illegal.
Lance Crawford, 29, a loan officer in Andover, Minn., could accept the idea of some benefits for gay couples, but he draws the line at the institution of marriage.
"I don't agree with it based on science reasons alone," he says, calling homosexuality unnatural. "It just opens the door for even more things in the future" that could undermine the country's morality.
Since 1998, voters in 30 states have approved constitutional amendments that define marriage as between a man and a woman, and eight other states have enacted statutes barring gay marriage. Nine states and the District of Columbia have moved to legalize same-sex marriages.
Since the issue was engaged in earnest less than two decades ago, public opinion has been reshaped. In 1996, a Gallup Poll found Americans opposing same-sex marriage by an overwhelming 68 percent to 27 percent. Now, an analysis of aggregated polls during the past decade shows movement toward support in every age group and every region.
In the new survey, the only age group in which a majority opposes same-sex marriage are those 65 and older, and the only region with majority opposition is the South.
Last month's elections may have marked a turning point. Maine, Maryland and Washington became the first states to approve same-sex marriage by popular vote. A fourth state, Minnesota, defeated a proposed constitutional amendment that would have defined marriage as between a man and a woman.
There were other groundbreaking votes as well. In January, Wisconsin's Tammy Baldwin will become the first openly gay member of the U.S. Senate. Arizona's Kyrsten Sinema will be the first openly bisexual member of the U.S. House. A record four state legislatures in California, Colorado, Oregon and Rhode Island are poised to be led by openly gay Assembly speakers.
"We saw a landslide for equality across this country," says Chad Griffin, president of the Human Rights Campaign, the nation's largest political group representing lesbian, gay, bisexual and transgender interests. "There really is no other way to describe what happened on Election Night other than it was a watershed moment for equality in this country."
Brian Brown, president of the National Organization for Marriage, argues that the ballot measures legalizing same-sex marriage passed "in the deepest of deep-blue states." They are a spur to opponents, including his group, as they prepare for future battles.
"The biggest lesson for us," he said, "is we will never again allow us to be outspent in this way."
One possible reason behind changing attitudes: Nearly eight in 10 adults say they know a relative, friend or co-worker who is gay, and most describe that relationship as a close one. In the survey of gay men and lesbians, 73 percent say they are generally open about their sexual orientation with other people; 26 percent say they aren't.
"When you have a brother or sister or relation, a friend, whatever, it's a personal thing," says poll respondent Mike Haigerty, 49, of Indianapolis. The director of religious education at a Catholic parish, he opposes same-sex marriage as a "slippery slope" that would separate sex from procreation in violation of his church's teachings.
Still, he says, "One of my closest friends has a younger brother who has a partner. I see their family at Christmas. Doug and John are great guys. We just don't talk about it. It's like 'don't ask, don't tell.' " When the issue is seen through the perspective of people you know, Haigerty says, "that really pulls on people's hearts."
Asked in an open-ended question why they back gay marriage, about one in 10 supporters cite friends or family members who are gay or lesbian. A third volunteer that love and happiness should matter, not sexual orientation, and a third cite equal rights. Fourteen percent say the issue shouldn't be one that is up to the government or them.
Asked why they are against gay marriage, nearly half of opponents say it violates the Bible's precepts or their religion; 16 percent call it morally wrong. Six percent say civil unions should be enough.
Indeed, a wide national consensus has emerged on granting same-sex couples the economic rights that civil unions generally guarantee. In the poll, more than three of four Americans support inheritance rights for same-sex couples and say gay men and lesbians should have access to their partners' health insurance and employee benefits.
Even among the demographic groups most strongly opposed to gay marriage seniors, conservatives, Republicans and frequent churchgoers a majority endorse those rights.
The national poll of 1,015 adults, taken Nov. 26-29, has a margin of error of plus or minus 4 percentage points. At the end of the survey, 4.9 percent said in response to a question that they were gay, lesbian, bisexual or transgender. That's higher than the 3.5 percent response Gallup typically has gotten, possibly because the previous survey questions dealt mostly with gay rights.
A separate poll was taken Nov. 27-29 of 251 adults who had identified themselves as lesbian, gay, bisexual or transgender in the Gallup daily tracking poll this year. The margin of error for that survey is plus or minus 6 percentage points.