A same-sex marriage supporter waves a rainbow flag in front of the U.S. Supreme Court. (SAUL LOEB/AFP/Getty Images)

Half of all Americans believe that gay men and lesbians have a constitutional right to marry, according to a new Washington Post-ABC News poll in which a large majority also said businesses should not be able to deny serving gays for religious reasons.

Fifty percent say the U.S. Constitution's guarantee of equal protection gives gays the right to marry, while 41 percent say it does not.

Beyond the constitutional questions, a record-high 59 percent say they support same-sex marriage, while 34 percent are opposed, the widest margin tracked in Post-ABC polling.

The poll was conducted in the wake of a series of rulings by federal judges that state bans on same-sex marriage and prohibitions on recognizing marriages performed elsewhere are unconstitutional.

The judges have said they relied on the reasoning in the Supreme Court’s 5 to 4 decision in June that struck down a key part of the Defense of Marriage Act, which withheld federal benefits from, and recognition of, same-sex couples married in states where such unions are legal. Since then, the highest courts in New Jersey and New Mexico have said same-sex couples must be allowed to marry in those states, and the six federal court decisions have come in some of the most conservative states, including Oklahoma and Utah.

Support for gay rights more entrenched across the country

In the 33 states that prohibit same-sex marriage, 53 percent of those polled support allowing it, while 40 percent oppose doing so.

Apart from supporting the policy, Americans are slightly more ambivalent about whether the Constitution guarantees gays the right to marry.

According to the poll, public opinion is more unified on recent proposals that would allow businesses to refuse serving gays and others based on the religious convictions of the business owner. Nearly seven in 10 respondents say businesses should not be allowed to refuse service to gays. On this question, majorities across partisan lines said businesses should not be allowed to deny service.  Last week, Arizona Gov. Jan Brewer (R) vetoed a measure that would have allowed businesses to refuse service to customers based on religious grounds.

“She did the right thing in vetoing that,” said Charles Musser of Marana, Ariz., who said that he opposes same-sex marriage and adoption rights for gays but that he thought the legislation was ill-conceived. If they passed that law, “that would open the door to all kinds of discrimination,” he said.

Support for same-sex marriage has changed more rapidly than almost any social issue in the past decade. In a Post-ABC poll in March 2004, 38 percent said same-sex marriage should be legal, while 59 percent said it should not, the same percentage now in favor of allowing gays to marry.

The shifting attitudes extend beyond issues of marital rights to more basic beliefs about the nature of homosexuality and its implications for child rearing. Nearly eight in 10 say that gays can parent as well as straight people, up from just below six in 10 in a 1996 Newsweek survey.

Sixty-one percent support allowing gays to adopt a child, up from 49 percent in 2006 and 29 percent in a 1992 poll by Time magazine and CNN. More than twice as many people consider being gay as “just the way they are,” rather than something they chose.

Despite the changing views, deep chasms remain along religious, generational and political lines. Six in 10 evangelical Protestants oppose same-sex marriage, while about six in 10 Catholics, non-evangelical Protestants and eight in 10 with no religious affiliation support it. Three-quarters of Americans younger than 30 support same-sex marriage, while less than half of seniors say the same.

Although support for such unions has grown to clear majorities among Democrats (70 percent) and independents (61 percent), Republicans have moved at a slower pace. Fifty-four percent of Republicans oppose same-sex marriage in the new poll, while 40 percent approve of it.

“I just don’t believe in the marriage thing; the Bible says that isn’t right," said Musser, who opposed the Arizona legislation on the religious rights of businesses.

Republicans are split along ideological and religious lines. Support for allowing same-sex marriage is lowest, below one-third or less, among conservatives and evangelical Protestants.

Among Republicans who say people are born gay (half say this), 64 percent support same-sex marriage, 61 percent say the Constitution provides the right to such unions and 70 percent favor allowing gays to adopt.

“Even though I was brought up very conservatively and very religiously, I don’t care what sexual orientation people are,” said Lilly Telatycki of Surprise, Ariz., who asked to be identified by her maiden name, saying she feared being harassed for that view. Telatycki, who usually votes Republican, said she thinks the party is spending too much time on the issue.

The poll also shows divisions among Democrats along racial and class lines. Support for same-sex marriage peaks at nearly eight in 10 white Democrats, and an even larger proportion with incomes more than $50,000 favor such unions. Support is lower, just over six in 10, among non-whites and those with lower incomes.

Robert Barnes contributed to this report.