All eyes on swing-voter Anthony Kennedy as Supreme Court wrestles with gay marriage

The Supreme Court appeared sharply divided on Tuesday along ideological lines on whether the Constitution guarantees a right to same-sex marriage, but Justice Anthony Kennedy, a pivotal vote, seemed open to legalizing gay marriage nationwide.

In 2-1/2 hours of arguments, the justices peppered lawyers on both sides of the issue with questions in the landmark case.

At one point, a protester shouted that the justices would "burn in hell" if they backed gay marriage, then he was dragged screaming from the packed courtroom by police.

Kennedy, a conservative who often casts the deciding vote in close cases and has a history of backing gay rights, appeared to be tipping toward recognizing a nationwide right to marriage based on his emphasis on the nobility and dignity of same-sex couples.

He also challenged one of the key assertions made by states that ban gay marriage: that same-sex couples do not have the same bonds with their children as straight couples.

Kennedy said little during the second part of the argument, which focused on whether states are required to recognize same-sex marriages from out of state. That could indicate he did not think the court would need to reach that question because it would rule that gay couples have a right to marry.

At one point Kennedy told attorney John Bursch, arguing in favor of state bans, that his arguments “assume same-sex couples cannot have a more noble purpose” when deciding to marry.

Earlier in the argument, Kennedy sounded conflicted about the centuries of history in which marriage has been limited to opposite-sex couples.

"This definition has been with us for millennia, and I think it's very difficult for this court to say we know better," Kennedy said.

A lively crowd estimated at more than 1,000 people, with those favoring legalized gay marriage outnumbering those opposed, gathered outside the white marble courthouse as the justices heard arguments in the case, known as Obergefell v. Hodges.

The justices, taking up a contentious social issue in what promises to be the year's most anticipated ruling, are due to deliver a decision by the end of June on whether gay marriage will be legal nationwide.

The court's four liberal justices seemed willing to vote in favor of gay marriage, while the court's conservatives, including Chief Justice John Roberts, appeared inclined to back the right of states to restrict the definition of marriage.

Roberts gave no sign that he is likely to join the liberals. He, like Kennedy, stressed the swift changes in attitudes to gay marriage and questioned whether it was the court’s role to decide it once and for all.

“Closing the debate can close minds,” Roberts said.

Other conservatives also posed tough questions to Mary Bonauto, the lawyer arguing in favor of same-sex marriage.

Justice Antonin Scalia questioned whether religious ministers who oppose same-sex marriage would be required to officiate over ceremonies. Similarly, Justice Samuel Alito asked whether incestuous or bigamous relationships could be allowed if the court embraced same-sex marriage.

The most persistent questions in favor of gay marriage came from Justice Elena Kagan. She questioned the notion that restricting marriage to opposite-sex couples would help encourage stable environments for children. She noted that many gay couples want to adopt children and often want the benefits of marriage.

If gay marriage is allowed, more people would be in a position to adopt, Kagan said.

“How is it not a good thing?” she asked.

CASE CENTERS ON BANS IN FOUR STATES

The arguments center on gay marriage bans in Kentucky, Michigan, Ohio and Tennessee, four of the 13 states that currently prohibit it.

Public support for gay marriage has steadily grown in recent years and is particularly strong among younger Americans.

Before gay marriage became legal in Massachusetts in 2004, it was not permitted in any state. Now it is allowed in 37 states and Washington, D.C.

The arguments were divided into two parts.

The first was on whether the Constitution's guarantees of due process and equal protection under the law mean states must allow gay couples to marry. The second concerned whether states must recognize same-sex marriages occurring out-of-state.

Opponents say same-sex marriage legality should be decided by individual states, not judges. Some opponents argue it is an affront to traditional marriage between a man and a woman and that the Bible condemns homosexuality.

There was a lively debate outside the courthouse.

Gay marriage advocates held up signs with slogans including "Love for all" and "America is ready for freedom to marry." A smaller but vocal group of people against gay marriage held signs including one calling gay sex sinful and another stating, "Satan rules over all, the children of pride."

Darren Nimnicht, 63, and Tom Cicero, 62, a couple from New York married for seven years, joined the demonstration.

"It's ensuring our rights to be treated like every other citizen in this country," Nimnicht said.

President Barack Obama's administration argued on the side of same-sex marriage advocates. He has said he hopes the court issues a ruling preventing states from banning gay marriage.

(Additional reporting by David Ingram, Joan Biskupic and Elvina Nawaguna; Editing by Will Dunham)