Tuesday’s historic arguments before the Supreme Court left the strong impression that a majority of the nine justices is not yet willing to establish a nationwide, constitutional right to marry for all same-sex couples, even if the court allows such marriages to occur in California or a subset of states.

The justice widely considered to be the swing vote — Anthony M. Kennedy — appeared to be searching for middle ground during the arguments in a case that could bring the court’s most important social policy decision in decades. But Kennedy also held out the possibility that the court would not rule on the merits of the case at all.

With throngs of gay marriage supporters and opponents assembled outside the courthouse — and swarms of media and spectators within — the justices spent 80 minutes evaluating whether they should effectively legalize same-sex marriages around the country or take any of a number of legal steps at their disposal that would fall short of that sweeping outcome.

The attorney arguing in favor of supporters of traditional marriage, Charles J. Cooper, attempted to persuade a majority of the high court that California voters acted constitutionally when they approved a 2008 state ballot initiative, known as Proposition 8, banning gay couples from marrying.

Cooper said the voters’ decision not only represented the will of the people, but furthered a legitimate governmental interest because it promoted procreation — a process that is biologically impossible for same-sex couples.

In an important and potentially telling exchange, Kennedy expressed skepticism about the argument that child-rearing would be harmed as a result of legalized gay weddings. He cited a legal brief finding that about 40,000 children of same-sex couples in California support full marriage rights for their parents.

“The voice of those children is important in this case, don’t you think?” Kennedy said.

With that argument, Kennedy joined the members of the court’s liberal wing in aggressively questioning the notion that legalization of gay unions would harm procreation or, for that matter, any governmental interest. The court’s conservatives largely remained silent on that point.

Justice Stephen G. Breyer said that if procreation is the primary governmental interest in banning same-sex unions, as Cooper contended, then unions between sterile heterosexual couples also could be banned.

Justice Elena Kagan latched onto Breyer’s theme and said that unions between couples over 55 years of age — who might no longer be fertile — also might be prohibited under Cooper’s rationale. “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,” she said, prompting laughter in the courtroom.

While Kennedy appeared skeptical of the procreation argument advanced by Cooper, he also made clear that he is highly uncomfortable with the most sweeping of the arguments made by Theodore B. Olson, the attorney representing two same-sex California couples in the case.

Olson, a veteran Supreme Court advocate, argued that the Constitution’s Equal Protection Clause should require same-sex marriage to be legalized not just in California, but around the country — including in the roughly three dozen states that have constitutionally or statutorily banned such unions.

Kennedy indicated that would be a step too far for him.

“The problem with the case is that you’re really asking … for us to go into unchartered water,” he said in remarks echoed by the court’s conservative justices during other parts of the arguments.

Justice Samuel A. Alito Jr. said if the court went as far as Olson suggested, it would be legalizing a practice that is “newer than cellphones or the Internet.”

Justice Antonin Scalia said he has not made up his mind one way or the other about the constitutionality of gay marriage, but suggested he is reluctant “to impose this on the whole country.”

Less Sweeping Options

If the pivotal Kennedy appeared to be searching for a middle ground, one potential option would be a separate legal path that the justices debated Tuesday: finding that supporters of traditional marriage lack the standing to bring their appeal in the first place. In the California case, Hollingsworth v. Perry, the petitioners defended Proposition 8 because state officials would not do so.

Though many legal observers have considered that an outside option — because the court could have simply agreed not to take up the California case at all — the justices spent about a quarter of the argument debating the issue. All but two, Alito and Clarence Thomas, questioned Cooper about whether his clients had a right to be at the Supreme Court at all, and Kennedy and other justices may decide that they do not. Kennedy pointedly called it a “substantial question.”

If the court agrees that the petitioners have no standing, same-sex couples would likely have the right to marry in California immediately, but the decision would be limited to that state. A high court precedent on the constitutional merits of same-sex marriage would be put off for another day.

Another potential outcome — one supported by the Obama administration — would be for the court to legalize same-sex unions only in the handful of states, such as California, that already provide same-sex couples with marital benefits but do not go so far as to call those unions “marriages.”

Solicitor General Donald B. Verrilli Jr. argued in favor of that option, which was taken by the 9th U.S. Circuit Court of Appeals in San Francisco, but he faced considerable skepticism from liberal and conservative justices alike.

Chief Justice John G. Roberts Jr. accused the administration of putting forth an “internally inconsistent” position. Alito pointedly asked Olson if he was “seriously arguing” that the administration’s position would be different if the case had come from a state that currently offers no marriage benefits to gay couples, such as Utah, as opposed to one that offers nearly all benefits, such as California.

“I don’t think you can have it both ways,” Alito said.

Meanwhile, Kennedy wondered aloud whether the best option for the court would be to dismiss the case outright and leave its questions for a day in the future when more information about gay marriage is available. “I just wonder if the case was properly granted,” he told Olson at one point.

Public Opinion Ahead of Court

Public opinion is changing rapidly in favor of same-sex marriage rights, with one recent poll showing that 6 in 10 Americans — an all-time high — now believe it should be legal for gay couples to wed.

Last May, Barack Obama became the first president to endorse gay marriage. Last week, Obama’s former secretary of state and chief rival for the 2008 Democratic presidential nomination, Hillary Rodham Clinton, announced that she also supports same-sex marriage.

Senators from both sides of the aisle, including Democrats Claire McCaskill of Missouri, Jon Tester of Montana and Mark Warner of Virginia, and Republican Rob Portman of Ohio, also declared their support for gay marriage ahead of Tuesday’s arguments.

While the subject of gay marriage remains a culturally explosive issue in many parts of the country, congressional Republicans have generally steered clear of the Proposition 8 case, both because of the shifting politics surrounding it and the fact that it is primarily a state, rather than a federal, issue.

One prominent congressional conservative, however, said the Supreme Court would be straying from the Constitution if it agreed to provide constitutional marriage rights for same-sex couples.

“The Constitution never contemplated marriage being anything other than between a man and a woman,” Rep. Steve King, R-Iowa, said in a statement. “And for the United States Supreme Court to come to an opposite conclusion would mean, I think, a real distortion of the Constitution, which is a contractual guarantee between each of the generations.”

The Supreme Court is expected to issue its opinion in the case in late June.

On Wednesday, the justices will tackle another high-profile gay marriage case when they will evaluate the constitutionality of a portion of the 1996 Defense of Marriage Act, which defines marriage for federal purposes as the union of a man and a woman.