THE SUPREME COURT has teed up what could be one of the weightiest civil rights rulings in years. It decided last week to hear arguments on two cases regarding same-sex marriage — one on California’s Proposition 8, which bans same-sex marriage, and another on the Defense of Marriage Act (DOMA), which denies federal benefits to legally married same-sex couples. Advocates of same-sex marriage celebrated the arrival of this issue to the highest court, understandably. But some, also understandably, worry about the possible outcome.

Recent developments already had given advocates of same-sex marriage many reasons to celebrate. Two federal appeals courts struck down the worst parts of DOMA this year. Then, in November, voters in three states, including Maryland, chose to legalize same-sex marriage, the first time such measures have prevailed at the ballot box; a fourth state voted down a ban on same-sex marriage. Now, with increasing evidence of growing social acceptance, some hope that in 2013 the run of victories will be capped with a sweeping ruling from the justices proclaiming marriage equality to be constitutionally guaranteed under the 14th Amendment.

Yet there is reason for caution. It is unclear, at best, whether that wave of social acceptance is moving across the country or destined to crash ineffectually on the borders of socially conservative states. It was only in May that voters in North Carolina approved an amendment to their state constitution barring same-sex marriage. A sweeping court ruling in favor of same-sex marriage could produce a backlash. A forceful California Supreme Court decision, after all, led to Proposition 8.

It should be little surprise, then, that the two appeals courts that ruled on DOMA this year did so narrowly, carefully explaining that their findings could not be interpreted as hostile to state-level bans on same-sex marriage. Dispensing with Proposition 8, another federal appeals court also attempted to restrain the constitutional scope of its decision, though the reasoning was a stretch.

In striking down both laws, the Supreme Court could adopt the logic of the various appeals courts, or it could find other legally acceptable ways to avoid a sweeping ruling just yet. Same-sex couples could then marry in California, and married same-sex couples across the country could obtain federal benefits — but other states would have more time to consider their own policies on the issue. Such an outcome might disappoint those who see no justification for continued discrimination. But it would nevertheless be an important step in the right direction.

Of course, the justices have a third option: upholding DOMA, Proposition 8 or both. Choosing that way would be a historic mistake. The court’s job is to determine judges’ proper role in moving the country away from discrimination, not to enshrine that discrimination in constitutional doctrine. However the court rules, its decision will be a guidepost on a road that eventually ends in legal and social acceptance of equal rights. It should not point backward.