A decision by a federal judge in Utah ordering the state to immediately permit same-sex marriages is setting the stage for what could become the ultimate constitutional showdown over gay marriage.

On Tuesday, Utah officials asked US Supreme Court Justice Sonia Sotomayor to temporarily halt the federal judge’s Dec. 20 ruling requiring the state to permit same-sex marriages despite a state constitutional amendment outlawing the practice. Justice Sotomayor responded by requesting briefs from lawyers representing six gay couples challenging the Utah ban. Those briefs are due on Friday.

In the meantime, more than 900 same-sex couples have used the judge’s ruling – and his refusal to postpone it – to obtain once-forbidden marriage licenses in Utah.

Although the immediate question is whether the judge’s same-sex marriage order should be stayed pending further appeals, the underlying issues will require Sotomayor – and perhaps the entire high court – to address the single most significant question in the legal debate over gay marriage. The question is whether same-sex couples have a fundamental right to marry under the US Constitution.

The justices intentionally avoided answering that very question in last June’s landmark gay rights decision striking down part of the federal Defense of Marriage Act (DOMA).

The high court voted 5 to 4 to invalidate a portion of DOMA because the majority justices said it violated the equal rights of same-sex couples who were legally married under state law. Because particular states had resolved to confer equal status to married couples regardless of sexual orientation, the federal government could not impose its own counter-requirements that would disrupt or belittle a state’s decision, the majority justices said.

What the high court did not decide was whether DOMA violated a fundamental right of same-sex couples to marry.

Nonetheless, the judge in Utah, US District Judge Robert Shelby, cited the June high court opinion as support for his conclusion that a fundamental right to marry applies to all Americans regardless of sexual orientation.

“[The DOMA decision] does not answer the question presented here, but its reasoning is nevertheless highly relevant and is therefore a significant doctrinal development,” Judge Shelby wrote in his decision.

He found that gay couples in Utah enjoy a fundamental right to marry and a fundamental right to have their marriages recognized by their state government.

If upheld by the high court, Shelby’s decision would require recognition of same-sex marriages nationwide and invalidate more than 30 state constitutional amendments and statutes banning same-sex marriages.

In their request for a stay from the high court, Utah officials maintain that there is no fundamental right to same-sex marriage under the US Constitution, and that it is well within in the power of the states to decide for themselves whether men can marry men and women can marry women or whether to restrict the institution to opposite-sex couples.

The Utah legislature approved a statute in 1977 and, again, 2004 barring same-sex marriages, and in 2004, 66 percent of the voters supported a constitutional amendment restricting marriage to one man and one woman.

Utah officials argue that the judge overstepped his federal authority by issuing a decision that undercuts and belittles the sovereign authority of Utah and its citizens to govern themselves without facing federal interference.

“Every marriage performed uniting persons of the same sex is an affront to the sovereignty of the State and to the democratically expressed will of the people of Utah,” the Utah brief says in part.

In essence, Utah officials are urging the justices to extend the same logic used in their analysis of last year's DOMA case. If the federal government cannot intrude on a state’s decision to recognize same-sex marriages, why should the federal government (via a district judge) now be permitted to intrude because a state chooses not to recognize them?

It would be unnecessary to answer that question if the US Constitution protects a fundamental right to same-sex marriage. But if it doesn’t, will it be up to each state to decide for itself whether to recognize same-sex marriages?

The Utah brief notes that four justices, all members of the court’s conservative wing, appear to support the view that the states have the power to decide. What is not clear at this point is how Justice Anthony Kennedy views the issue. His vote will likely decide the matter.

The more immediate issue is whether Shelby’s ruling should be stayed as the appeals move forward. Such stays are routinely issued in major cases but are not required.

It is clear from Shelby’s original ruling that he sees no harm in hundreds of same-sex couples marrying while the case works its way through the courts.

“The State of Utah has provided no evidence that opposite-sex marriage will be affected in any way by same-sex marriage,” he wrote in his opinion. “In the absence of such evidence, the State’s unsupported fears and speculations are insufficient to justify the state’s refusal to dignify the family relationships of its gay and lesbian citizens.”

Utah officials had also asked a federal appeals court to grant a stay. The two-judge panel granted expedited consideration of the appeal, but refused to halt the ongoing marriages.

“We conclude a stay is not warranted,” the appeals court panel said, without further explanation.

Utah directed its high court appeal to Sotomayor, who is designated to handle such matters from Utah and other states within the jurisdiction of the 10th US Circuit Court of Appeals. She can decide the stay request on her own or refer it to the entire court.

In its brief to the high court, Utah says the state has suffered and will continue to suffer irreparable harm from Shelby’s refusal to stay the decision.

“The district court’s extraordinary decision to overturn Utah’s marriage laws – and its refusal even to stay its order pending further review – places in jeopardy the democratic right of millions of Utahns to choose for themselves what marriage will mean in their community,” the brief says.

If the judge’s decision is overturned by a higher court, it adds, the state will face the difficult task of having to “unwind the marital status of same-sex unions performed before reversal of the district court’s decision.”

Same-sex couples and their children “will likely suffer dignitary and financial losses from the invalidation of their marriages” if the decision is overturned on appeal, the state argues.