By Greg Stohr, Bloomberg News (TNS)

WASHINGTON — When three of his U.S. Supreme Court colleagues said two years ago that same-sex marriage wasn’t a constitutional right, Chief Justice John Roberts left himself room to maneuver.

Roberts declined to join that group, and that decision will put him in focus Tuesday when the court hears arguments in a historic clash that may legalize gay marriage nationwide.

With Roberts uncommitted, some advocates are hoping that the nation’s highest judicial officer will place his imprimatur on a pro-marriage ruling. Should the court back same-sex marriage it would cap a transformation in the rights of gays over the past dozen years, bringing weddings to the last 14 states where they are banned.

“His vote is in play,” said Judith Schaeffer, vice president of the Constitutional Accountability Center, which backs marriage rights. “I don’t think people should write him off.”

Same-sex marriage opponents are skeptical, saying Roberts’s record during his decade as chief justice points strongly toward support for state bans. Gay-rights advocates say the chief justice nonetheless may be swayed by what they see as the tide of history toward marriage equality.

The 2013 ruling, which struck down a federal law that denied benefits to married same-sex couples, has stoked expectations that the court was preparing to make gay weddings legal throughout the country. Even Justice Antonin Scalia predicted in dissent that the five-member majority — four Democratic appointees, plus Justice Anthony Kennedy — was poised to take that step.

That sense grew over the last seven months as the court let gay marriage begin in 17 new states. In February, Justice Clarence Thomas said an order that let gay marriage briefly begin in Alabama “may well be seen as a signal of the court’s intended resolution” of the issue.

Roberts would be the sixth vote, unnecessary to secure the victory but valued for its symbolic significance.

His support would “add to the emerging sense that same-sex marriage is not a partisan issue,” said Michael Dorf, a constitutional law professor at Cornell Law School who filed a brief backing marriage rights. “That would help in getting the decision complied with in the parts of the country where public opinion is against same-sex marriage.”

The hints Roberts dropped two years ago weren’t exactly favorable for gay-rights advocates. He blasted Kennedy’s majority opinion and its conclusion that the federal law was aimed at stigmatizing same-sex marriage.

Perhaps more ominously, Roberts said Kennedy’s reasoning actually argued against a constitutional right by pointing to the traditional power of the states to define marriage.

“That power will come into play on the other side of the board in future cases about the constitutionality of state marriage definitions,” Roberts wrote in the case, U.S. v. Windsor.

Gene Schaerr, a lawyer involved in the defense of Utah’s gay-marriage ban, said Roberts’s opinion makes him a likely vote to uphold the state prohibitions.

“For him to rule in favor of the right to same-sex marriage would really be inconsistent with his position in Windsor,” Schaerr said.

Gay-marriage backers aren’t convinced. They note that Roberts didn’t sign onto the more pointed dissent from Scalia, who accused the majority of writing “legalistic argle-bargle.” Nor did he join Justice Samuel Alito in saying flatly that “the Constitution does not guarantee the right to enter into a same-sex marriage.”

Roberts “was preserving a clean slate for himself for the ultimate case,” Schaeffer said.

More recently, the chief justice declined to join Scalia and Thomas in publicly dissenting from orders that let same-sex marriage go forward in South Carolina, Florida and Alabama while the high court considers the issue. Roberts and Alito both made no comment.

And Roberts might have been behind the decision in October not to review pro-marriage rulings by three federal appeals courts. The Supreme Court takes up cases only when four justices want to do so, and the court generally doesn’t disclose who voted which way.

The high court didn’t agree to intervene until a different federal appeals court had ruled against marriage rights in cases from Michigan, Kentucky, Ohio and Tennessee. The justices will hear two hours and 30 minutes of argument starting at 10 a.m. Eastern on Tuesday.

Gay-rights advocates say the bans in those states deprive same-sex couples of a fundamental right and unconstitutionally treat them differently than heterosexuals. The states say the definition of marriage should be left to the voters.

“What it’s about is who gets to decide that question,” said former Michigan Solicitor General John Bursch, one of two lawyers who will be arguing for the states. “Is it the people acting through the democratic process, or is it the federal courts?”

One possibility is that Roberts could join the majority and try to write a relatively narrow opinion for the group, perhaps one aimed at protecting the religious rights of people who object to same-sex weddings.

Schaerr discounted that possibility, saying he doubts Roberts would cast “what amounts to a dishonest vote just so he can control what the opinion says.”

Still, chief justices have been known to join major rulings that don’t perfectly align with their previously expressed views. Dorf points to the example of William Rehnquist, who wrote the 2000 decision reaffirming the landmark 1966 Miranda ruling and its requirement that police advise suspects of their rights.

Roberts himself joined the court’s four Democratic appointees in 2012 to uphold the core of President Barack Obama’s health care law.

“It is conceivable that he could provide the sixth vote for institutional reasons having to do with the court’s legitimacy and making the decision appear more legal and less political,” said Douglas Laycock, a University of Virginia law professor who filed a brief backing marriage rights. “I do not think that is very likely, but it wouldn’t be astonishing.”

With same-sex weddings finding increasing acceptance in public opinion, Schaeffer says she hopes broader forces will persuade Roberts to join a majority decision favoring marriage rights.

“Does he want to be a little footnote to history?” she asked. “Or does he want to be on the right side of history and the right side of the Constitution?”

(c)2015 Bloomberg News, Distributed by Tribune Content Agency, LLC.

Photo: Opponents and proponents of gay marriage at a rally in the state capitol, March 2004. (Kentucky Photo File/Flickr)