Historic day as court hears marriage case.

Byline: Mark Sherman

WASHINGTON -- Pivotal Justice Anthony Kennedy, whose vote could decide the same-sex marriage issue for the nation, did not tip his hand Tuesday in historic arguments at the Supreme Court. But Kennedy's record on the issue could give encouragement to gay and lesbian couples.

As advocates and protesters demonstrated outside, the author of the court's three prior gay rights rulings talked about the touchstones of dignity and concern for children in same-sex households that drove his favorable earlier opinions.

But he also worried about changing the definition of marriage from the union of a man and a woman, a meaning that he said has existed for ''millennia-plus time.''

''It's very difficult for the court to say 'We know better''' after barely a decade of experience with same-sex marriage in the United States, Kennedy told Mary Bonauto, a lawyer representing same-sex couples.

The 78-year-old justice's likely role as a key, perhaps decisive vote was reinforced during arguments that lasted 21/2 hours in a rapt courtroom and appeared to divide the court's liberal and conservative justices over whether the Constitution gives same-sex couples the right to marry. Those couples can do so now in 36 states and the District of Columbia, and the court is weighing whether gay and lesbian unions should be allowed in all 50 states.

''Samesex couples say, of course, 'We understand the nobility and the sacredness of marriage. We know we can't procreate, but we want the other attributes of it in order to show that we, too, have a dignity that can be fulfilled,''' Kennedy said in an exchange with lawyer John Bursch, who was defending the state marriage bans

Later, Kennedy also seemed concerned about adopted children in same-sex households if only one partner is considered a parent. ''Under your view, it would be very difficult for same-sex couples to adopt those children,'' Kennedy said.

Tuesday's arguments offered the first public indication of where the justices stand in the dispute over whether states can continue defining marriage as the union of a man and a woman, or whether the Constitution gives gay and lesbian couples the right to marry. In the court's last look at same-sex marriage in 2013, the justices struck down part of the federal anti-gay marriage law. Federal courts with few exceptions have relied on Kennedy's opinion in that case to invalidate gay marriage bans in state after state.

The court divided 5-4 in that case, with...