WASHINGTON -- The Supreme Court Tuesday dived into a historic gay-rights debate that could soon lead to resumption of same-sex marriage in California, but the justices signaled they may not be ready for a major national ruling on the issue.

The issue was fundamental: Does the Constitution require that people be allowed to marry whom they choose, regardless of either partner's gender? The fact that the question was in front of the Supreme Court at all was startling, given that no state recognized same-sex unions before 2003 and 40 states still don't allow them.

Demonstrators on both sides crowded the grounds outside the court. Inside, a skeptical Justice Samuel Alito cautioned against a broad ruling in favor of gay marriage precisely because the issue is so new.

"You want us to step in and render a decision based on an assessment of the effects of this institution, which is newer than cellphones or the Internet? I mean, we do not have the ability to see the future," Alito said.

It was clear from the start of the 80-minute argument in a packed courtroom that the justices, including some liberals who seemed open to same-sex marriage, had doubts about whether they should even be hearing the challenge to California's Proposition 8, a same-sex marriage ban approved by voters in 2008.

Justice Anthony Kennedy, the potentially decisive vote, suggested the justices could dismiss the case with no ruling at all. Such an outcome would almost certainly allow same-sex marriages to resume in California but have no impact elsewhere.

There was no majority apparent for any particular outcome from Tuesday's arguments.

On the one hand, Kennedy acknowledged the recentness of same-sex unions. Charles Cooper, the lawyer for the defenders of Proposition 8, said the court should uphold the ban as a valid expression of the people's will and let the vigorous political debate over same-sex marriage continue.

But Kennedy pressed him to address the interests of an estimated 40,000 children in California with same-sex parents.

"They want their parents to have full recognition and full status. The voice of those children is important in this case, don't you think?" Kennedy said.

Yet when Theodore Olson, the lawyer for two same-sex couples, urged the court to support such marriage rights everywhere, Kennedy feared such a ruling would push the court into "uncharted waters."

President Barack Obama last year came out in support of same-sex marriage. But several members of the court also were troubled by the Obama administration's main contention that when states offer same-sex couples civil union rights of marriage, as California and eight other states do, they also must allow marriage. The other states are: Colorado, Delaware, Hawaii, Illinois, Nevada, New Jersey, Oregon and Rhode Island.

"So a state that has made considerable progress has to go all the way, but at least the government's position is, if the state has done absolutely nothing at all, then it can do as it will," Justice Ruth Bader Ginsburg said.

Polls have shown increasing support in the country for same-sex marriage. According to a Pew Research Center poll conducted in mid-March, 49 percent of Americans now favor allowing gays and lesbians to marry legally, with 44 percent opposed.

The court's first major examination of gay rights in 10 years continues Wednesday, when the justices will consider the federal law that prevents legally married same-sex couples from receiving a range of benefits afforded straight married people.

What Supreme Court justices said about same-sex marriage arguments

They want their parents to have full recognition the voice of these children is important in this case.'

-- Anthony Kennedy on the children of same-sex couples

There's considerable disagreement among sociologists as to ...the consequences of raising a child in a single-sex family, whether that is harmful to the child or not.' -- Antonin Scalia

Traditional marriage has been around for thousands of years," while "same-sex marriage is very new. It may turn out to be a good thing; it may turn out not to be a good thing.' -- Samuel Alito

The institution developed to serve purposes that, by their nature, didn't include homosexual couples.' -- John Roberts

I can just assure you, if both the woman and the man are over the age of 55, there are not a lot of children coming out of that marriage.' -- Elena Kagan, on argument that a key purpose of marriage is to foster procreation

We have five years of information to weigh against 2,000 years of history or more.' -- Kennedy

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