WASHINGTON — A cautious and conflicted Supreme Court on Tuesday seemed wary of a broad constitutional finding on whether same-sex couples have the right to marry, and some justices indicated it may be premature for them to intervene in a fast-moving, unsettled political environment.

Justice Anthony Kennedy, considered to be the pivotal vote on the issue, said the court was in “uncharted waters.” He questioned whether it should have even accepted the case, in which lower courts struck down California’s voter-approved Proposition 8, which restricted marriage to heterosexual couples.

The court’s historic review of same-sex marriage continues Wednesday with a more limited question: May Congress withhold federal benefits from same-sex couples married in those states where it is legal, such as Maine? Lower courts have said the Defense of Marriage Act of 1996 is unconstitutional because it treats legally married homosexual couples differently from heterosexual ones.

The cases have had a buildup befitting the consideration of one of the most divisive and politically charged issues in American life. Same-sex marriage did not exist anywhere in the world before 2000, and the national mood about such unions has changed so rapidly it has left politicians and the law behind.

Inside the court’s ornate chambers, some justices wanted to slow things down.

“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?” asked Justice Samuel Alito Jr. “We do not have the ability to see the future.”

Even Justice Sonia Sotomayor, whose questioning indicated she was skeptical of the reasons proffered for why gay couples should not be allowed to marry, seemed to think it might not yet be time for the court to make a bold decision.

“If the issue is letting the states experiment and letting the society have more time to figure out its direction, why is taking a case now the answer?” she asked.

Sotomayor’s question indicated the complicated nature of the case at hand.

Washington lawyer Charles Cooper is representing proponents of Prop 8 in defending the law, since California officials have refused. He said the court should respect the decision of California voters, who faced the “agonizingly difficult question” of whether to protect traditional marriage after the state Supreme Court had ruled gay couples could wed.

Theodore Olson, representing two California couples who plan to marry, wants Prop 8 overturned. But he also is pushing the court to find that the Constitution demands that the fundamental right to marry must be extended to same-sex couples nationwide.

Solicitor General Donald Verrilli Jr., representing the Obama administration, offered something of a middle ground. He said those states that offer gay couples benefits such as civil unions — fewer than 10 now — must take the next step and offer marriage.

The administration’s offer drew almost no interest from the justices. And from their comments, it was difficult to locate a majority of five for either of the other options.

Chief Justice John Roberts Jr. expressed a keen interest in whether the court might dispose of the case by finding that Cooper’s clients did not have the legal standing to bring the action. And Kennedy’s speculation that perhaps the court should not have accepted the case would in effect affirm the appeals court ruling.

Either of those would likely have the real-world impact of returning same-sex marriage to California, but not set a precedent for other cases.

Kennedy, who has written the court’s last two decisions that provided victories for gay-rights groups, seemed particularly torn.

“The problem with the case is that you’re really asking . . . for us to go into uncharted waters, and you can play with that metaphor: There’s a wonderful destination, it is a cliff,” said Kennedy. “We have five years of information to weigh against 2,000 years of history or more.”

On the other hand, he said, “There are some 40,000 children in California . . . that live with same-sex parents, and 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 also worried that a decision that Cooper’s clients did not have standing to bring the case would encourage state officials to simply not defend those citizen initiatives with which they disagree.

The debate about whether marriage should be extended to gay couples revealed a familiar ideological divide on the court.

Liberals such as Justice Elena Kagan seemed not to buy Cooper’s argument that the state’s interest in marriage was to foster responsible procreation and child-rearing.

“Suppose a state said that, because we think that the focus of marriage really should be on procreation, we are not going to give marriage licenses anymore to any couple where both people are over the age of 55,” asked Kagan. “Would that be constitutional?”

Cooper said that one of the partners might still be fertile, and Justice Antonin Scalia made a joke about the late Sen. Strom Thurmond, who fathered a child while in his 70s.

Kagan also pressed Cooper on his arguments that extending marriage benefits to gay couples could hurt heterosexual couples. “How does this cause and effect work?” she asked.

“We don’t believe that’s the correct legal question before the court,” Cooper said, “and the correct question is whether or not redefining marriage to include same-sex couples would advance the interests of marriage.”

Conservatives such as Scalia criticized Olson’s argument that there was a constitutional right to same-sex marriage. He repeatedly pressed Olson to tell him when it became unconstitutional to exclude gays from marriage — his point being that for years it was commonly understood there was no right.

After much back and forth, Olson finally said: “There’s no specific date in time. This is an evolutionary cycle.”

Roberts, too, said he was not sure whether there was any show of bias in excluding same-sex couples.

“When the institution of marriage developed historically, people didn’t get around and say ‘Let’s have this institution, but let’s keep out homosexuals,’” he said. “The institution developed to serve purposes that, by their nature, didn’t include homosexual couples.”

He also questioned Olson about his contention that it was inconsistent for California to provide gay couples with every other benefit of marriage but withhold the legal designation.

“So it’s just about the label in this case,” Roberts said.

“The label ‘marriage’ means something,” Olson responded.

Roberts did not give up: “If you tell a child that somebody has to be their friend, I suppose you can force the child to say, ‘This is my friend.’ But it changes the definition of what it means to be a friend.”

Olson repeatedly brought up the court’s 1967 decision in Loving v. Virginia, which swept away state laws prohibiting interracial marriage. “You could have said in the Loving case . . . you can’t get married, but you can have an interracial union. Everyone would know that that was wrong.”

Verrilli, the solicitor general, said the court should recognize that waiting to make a decision on same-sex marriage “is not a neutral act.”

“Waiting imposes real costs in the here and now,” Verrilli said. “It denies . . . to the parents who want to marry the ability to marry, and it denies to the children, ironically, the very thing that (Prop 8 supporters) focus on is at the heart of the marriage relationship.”

But Roberts said the administration’s position would carry more force if it was prepared to argue that same-sex marriage must be allowed nationwide.

“You (are) saying it’s got to happen right now in California, but you don’t even have a position about whether it’s required in the rest of the country,” he said.