From left, Kris Perry, Sandy Stier of Berkeley, Calif., and Jeff Zarrillo and Paul Katami of Burbank, Calif., arrive to visit the National Archives in Washington, Monday, March 25, 2013, to view the U.S. Constitution, a day before their same-sex marriage case is heard before the Supreme Court. (AP Photo/Jose Luis Magana)

WASHINGTON - The U.S. Supreme Court hears arguments beginning Tuesday on two laws critical to the rights of gay couples to marry, as new polls show a dramatic shift in the number of Americans who support overturning barriers to same-sex marriage.

Public opinion on the topic of gay and lesbian rights in the United States, a politically dangerous hot-button issue not so many years ago, has undergone one of the most rapid evolutions in recent history. According to a Pew Research Center poll conducted in mid-March, 49 per cent of Americans now favour allowing gays and lesbians to marry legally, with 44 per cent opposed. A decade, the numbers were heavily tilted in the opposite direction: 58 per cent opposed and just 33 per cent in favour.

As more gay and lesbian couples are in public view, Americans can see "there are real families who are impacted. People have seen there has been no negative impact (from gay marriage). It's only the exclusion from marriage that has a negative impact," said Jennifer Levi, professor of law at Western New England University.

The public opinion shift does not guarantee an outcome in favour of gay marriage in the conservative-leaning court. Gay marriage foes have expressed confidence that the justices will rule their way, and even some gay rights activists have worried that the court has taken up the issue too soon. Supporters of same-sex marriage hope for a ruling that will be the 21st century equivalent of the court's 1967 decision in Loving v. Virginia that struck down state bans on interracial marriage.

On Tuesday, lawyers representing two couples from California will try to persuade the nine Supreme Court justices to strike down the state's voter-approved ban on same-sex marriages and to declare that gay couples can marry nationwide.

Lawyers representing supporters of the California ban known as Proposition 8 will argue that the court should not override the democratic process and impose a judicial solution that would redefine marriage in the some 40 states that do not allow same-sex couples to wed.

The case before the high court came together four years ago when the two couples, Kris Perry and Sandy Stier of Berkeley and Paul Katami and Jeff Zarrillo of Burbank, agreed to be the named plaintiffs and become the public faces of a well-funded, high-profile effort to challenge Proposition 8 in the courts.

The fight began in 2004 when San Francisco Mayor Gavin Newsom ordered city officials to issue marriage licenses. Six months later, the state Supreme Court invalidated the same-sex unions. Less than four years later, however, the same state court overturned California's prohibition on same-sex unions. Then, in the same election that put President Barack Obama in the White House in 2008, California voters approved Proposition 8, undoing the court ruling and defining marriage as the union of a man and a woman.

The ballot measure halted same-sex unions in California. Roughly 18,000 couples were wed in the nearly five months that same-sex marriage was legal and those marriages remain valid in California.

The high-profile case has brought together two one-time Supreme Court opponents. Republican Theodore Olson and Democrat David Boies are leading the legal team representing the same-sex couples. They argued against each other in the Bush v. Gore case that settled the disputed 2000 presidential election in favour of George W. Bush. Opposing them is Charles Cooper, Olson's onetime colleague at the Justice Department in the Reagan administration.

The Obama administration has weighed in on behalf of the same-sex couples who brought the case, following President Barack Obama's declaration of support for same-sex marriage last year and his invocation of gay rights at his inauguration in January.

The case, having wound its way to the high court, could produce a number of rulings, ranging from upholding the California ban to striking it down in a fashion that would erase such bans nationwide. The court is not expected to rule before late June.

The case is being argued 10 years to the day after the court took up a challenge to Texas' anti-sodomy statute. That case ended with a forceful ruling prohibiting states from criminalizing sexual relations between consenting adults. Justice Anthony Kennedy, the swing vote on the divided court, was the author of the decision in Lawrence v. Texas in 2003, and he is being closely watched for how he might vote on the California ban.

Nine states and the district of Washington allow same-sex marriage, 12 others recognize "civil unions" or "domestic partnerships" that grant the same benefits without full rights of marriage. The 29 other states ban gay marriage in their constitutions.

Next up on Wednesday, the court will hear the first challenge it has accepted to the Defence of Marriage Act, the 1996 measure signed into law by former President Bill Clinton. Both he and his wife, potential 2016 Democratic presidential candidate Hillary Rodham Clinton, recently reversed course and now support same-sex marriage. The law, known as DOMA, forbids nationwide recognition of same-sex marriages and bars married gay and lesbian couples from receiving federal benefits.

Catherine Smith, associate dean at the Sturm College of Law at the University of Denver, sees a variety of reasons for the rapidly changing views on same-sex marriage, but foremost is the number of people who have publicly acknowledged they are gay. "That and the number of states that are recognizing this right (to marriage) is a huge factor."

But while public attitudes may be changing fast, there's still plenty of heavy and vocal opposition.

"I have always believed that gay people are human beings with human dignity who need to be treated with respect," Maggie Gallagher, co-founder of the National Organization for Marriage, said in a recent National Public Radio interview. "But that's different from having a foundational norm that says there is no morally relevant difference between same-sex and opposite-sex relationships and (that) if you see one, you're like a bigot who's opposed to interracial marriage."

And given that argument — a powerful one among religious organizations, churches and conservative voters in particular — a large chunk of Americans feel sure the high court will see things their way.

"We remain confident that the U.S. Supreme Court will uphold the ability of states and the federal government to define marriage as the union of a man and a woman, a definition that has served our nation well for hundreds of years," read a statement by Brian S. Brown, a 39-year-old father of eight who has raised millions of dollars from religious conservatives — especially his fellow Roman Catholics — to become the nation's leading opponent of same-sex marriage. He is president of the National Organization for Marriage and played a big role in passing California's Proposition 8.

News from © The Associated Press, 2013