The decision on whether to hear the case could be a hard call for both the court’s conservatives and liberals.

Usually, the justices are inclined to vote to hear a case if they disagree with the lower court ruling. The most conservative justices — Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr. — almost certainly think the 9th Circuit’s ruling was dubious. Scalia, for example, says the “equal protection” clause, added to the Constitution after the Civil War, aimed to stop racial discrimination and nothing more. He often insists the justices are not authorized to give a contemporary interpretation to phrases such as “equal protection.”

If Chief Justice John G. Roberts Jr. joins the other three, the conservatives would have the needed four votes to hear the Proposition 8 case…

Still, the court’s liberals also may hesitate. Justice Ruth Bader Ginsburg, though a leading women’s rights legal advocate, has said she thought the court made a mistake in the 1970s by moving too fast to declare a national right to abortion.