By Lawrence Hurley

WASHINGTON (Reuters) - The U.S. Supreme Court is set to decide within weeks whether to hear a major transgender rights case for the first time, a dispute involving which bathroom a Virginia high school student can use, but the justices have reasons to duck the issue.

The case involves a 17-year-old transgender student named Gavin Grimm, who was born female but identifies as male and is mounting a legal challenge to gain the right to use the boys' bathroom at his public high school in Gloucester County, Virginia.

The local school board is asking the justices to hear its appeal of an April 19 ruling by the Richmond-based 4th U.S. Circuit Court of Appeals that found that transgender students are protected under U.S. laws that bar sex-based discrimination.

If the high court refuses to hear the case, the justices would leave in place the groundbreaking appeals court ruling in favor of transgender rights that Grimm could use the bathroom of the student's choice. If the justices hear it, it would be one of the biggest cases of the 2016-17 term that opens Oct. 3.

The Supreme Court remains shorthanded with eight justices, split with four liberals and four conservatives, following the Feb. 13 death of Antonin Scalia. Legal experts say the court may have an incentive to dodge the issue, the latest front line in the battle over lesbian, gay, bisexual and transgender rights.

The high court so far has shown an inclination for its new term toward taking up technical, narrow cases, such as several on intellectual property rights, while it remains down one justice. This may be because the court is eager to avoid issuing 4-4 deadlocked rulings, which happened on four occasions after Scalia's death.

The Republican-led Senate has refused to consider confirmation of Merrick Garland, President Barack Obama's nominee to replace Scalia.

There are several reasons why the court could turn away the appeal, including the fact that there are other cases on the same issue pending in lower courts, meaning the justices could weigh in at a later date.

In one of those cases, a U.S. district court judge on Aug. 22 issued a nationwide injunction sought by Texas and 12 other states preventing the Obama administration from enforcing guidance telling schools to allow transgender students to use the bathroom of their choice.

The Supreme Court often lets novel legal issues like transgender bathroom rights percolate in lower courts before taking a case, as it did with gay marriage before ruling in 2015 to allow it nationwide.

The Supreme Court also frequently refuses to take cases in which the various regional federal appeals courts have not issued conflicting rulings. The ruling by the 4th U.S. Circuit Court of Appeals was the first of its kind.

Steven Shapiro, legal director of the American Civil Liberties Union, said the case "doesn't meet any of the traditional criteria" to warrant the court hearing the school board's appeal. The ACLU represents Grimm.

Conservatives who want the Supreme Court to hear the appeal point to the high court's action last month when it voted 5-3 to temporarily block the appeals court decision from going into effect, a move that prevented Grimm from using the boys' bathroom when the new school year began while the case remains under appeal.

"My gut is there's a good chance they will take this one," said Matt Sharp, a lawyer with the conservative Christian legal group Alliance Defending Freedom.

But Justice Stephen Breyer made clear that he cast the decisive vote to grant the school board's stay request merely as a courtesy to his colleagues. If the court were to hear the case, many think Breyer would vote with his fellow liberals, meaning the court could split 4-4 and leave in place Grimm's appeals court victory.

(Reporting by Lawrence Hurley; Editing by Will Dunham)