The lawsuit over same-sex marriage in Louisiana will enter its next phase on Friday, with one chapter unfolding in a federal courtroom in New Orleans and another one unspooling in Washington, D.C., where the U.S. Supreme Court will consider whether to render the whole case essentially moot.

Either way, Friday could be a watershed moment in the legal struggle over gay marriage, one that has played out rapidly over the past few years in lawsuits across the country.

In downtown New Orleans, lawyers for same-sex marriage proponents and the state of Louisiana, which has explicitly banned such unions since 2004, will trade blows in front of a panel of federal appeals court judges.

That court will be hearing arguments on an earlier ruling by New Orleans-based U.S. District Judge Martin Feldman, who in September became the first federal judge to uphold a state’s ban on same-sex nuptials since the Supreme Court struck down part of the federal Defense of Marriage Act in June 2013. Lawyers for the Forum for Equality Louisiana and a group of gay and lesbian couples will ask the appeals court to overturn Feldman’s decision.

Next up in front of the same three-judge panel will be lawyers arguing a nearly identical case from Mississippi. Then Texas. Advocates and reporters from all over the region will pack the courthouse, likely spilling into separate overflow rooms that have been arranged to accommodate the crowd.

“It is a huge moment for the LGBT community in Louisiana and Mississippi and Texas,” said John Hill, a former chairman of the forum’s board. “We’re having our day in court and being respected by the federal judiciary — if not our government.”

Still, even if the courts end up favoring same-sex marriage, Louisiana voters don’t appear to have warmed to the idea as quickly as the rest of the country. Exit polls conducted by national news organizations during the Senate elections in November showed only 24 percent of voters in the state thought it should be legal.

That tracks roughly with the overwhelming support the ban drew from voters when it passed in a statewide referendum a decade ago.

Nevertheless, the issue is quickly coming to a head in the courts, and gay rights proponents feel as confident as ever. While arguments go forward in New Orleans, the U.S. Supreme Court will consider whether to step in and decide the issue for the whole country, once and for all.

In a closed-door meeting on Friday, the nine justices of the court will vote on whether to take up a ruling from November, rendered by the U.S. 6th Circuit Court of Appeals in Cincinnati, upholding same-sex marriage bans in four different states: Ohio, Michigan, Kentucky and Tennessee.

It would be the first time the Supreme Court has considered the main question involved in all of the active lawsuits — whether banning same-sex marriage violates the Constitution.

Both sides of the Louisiana lawsuit have asked that their case be included with that appeal as well, even though the 5th Circuit Court of Appeals will still be hearing arguments on Friday and hasn’t had a chance to rule. It’s unusual for the Supreme Court to grant such a request, but not unprecedented.

It would come as a major surprise, however, were the Supreme Court to pass on same-sex marriage entirely.

The 6th Circuit came to the opposite conclusion from four other federal appeals courts that have ruled on similar cases, setting up the kind of split the high court typically feels compelled to resolve.

“In some parts of the country, there is a constitutional right for same-sex couples to get married, and in other parts of the country, there is not,” said Keith Werhan, a professor of constitutional law at Tulane University. “At some point, it becomes the responsibility of the court to weigh in.”

That said, Werhan acknowledged that he — and many other observers — have been surprised by the justices before, particularly when they let stand a set of appeals court rulings that cleared the way for gay marriage in five different states back in October.

Opponents of same-sex marriage were irate that the Supreme Court would allow the federal judiciary to decide the issue instead of voters. And gay rights activists had been confident the court would act to prevent a patchwork of different laws from one state to another.

The justices also may simply defer on Friday, putting off a decision on whether to take up any of the same-sex marriage cases until a later meeting.

Still, until now, there has been no split among federal appeals courts. Indeed, until Feldman’s ruling, federal judges had been unanimous in finding bans on same-sex marriage unconstitutional.

Most drew on the Supreme Court’s rationale in United States v. Windsor, a decision that struck down a portion of the federal Defense of Marriage Act that barred same-sex couples from receiving federal benefits, even if the states they lived in allowed them to wed. To treat married couples differently based solely on gender, most judges have concluded, violates the Fourteenth Amendment, which guarantees equal protection under the law.

Feldman, acknowledging his own position as an outlier, disagreed. “Windsor does little more than give both sides in this case something to hope for,” Feldman wrote, arguing that debates over the role and definition of marriage belong in the political realm rather than the courts.

Even considering the unbroken string of rulings to the contrary, the decision did not come as a complete surprise. Appointed by President Ronald Reagan, Feldman is known as a conservative judge.

Likewise, the 5th Circuit in New Orleans has among the most Republican appointees of any federal appeals court, although the makeup of the panel that will hear arguments in Louisiana’s same-sex marriage case has given some liberal analysts hope.

Judge James Graves is a recent Obama nominee. And while Judge Jerry Smith is known as a staunch conservative, Judge Patrick Higginbotham is seen as a potential swing vote, a conservative and a Reagan appointee but one who is flexible on social issues.

“You look at these judges and you say, ‘Well, that’s a panel that could go either way,’ ” said Kenneth Upton, a lawyer for the gay rights group Lambda Legal. Reading Higginbotham’s past opinions, Upton said, “I think this is a judge who will try to do the right thing and not bring an ideology to it. And that’s the best you can hope for.”