Francisco Kjolseth / Associated Press

Utah officials plan to ask the U.S. Supreme Court as early as Thursday to stop same-sex marriages in their state, a last-ditch effort to halt the parade of weddings since a federal judge struck down the state’s ban on such unions.

The state’s petition would go to Justice Sonia Sotomayor, who has jurisdiction over cases coming from Utah and neighboring states. She could either decide the issue herself or refer it to her colleagues. If she denies the state’s request, Utah officials could ask the full court to consider it. There’s no deadline for the justices to make a decision, but they typically act quickly on such requests.

Last Friday, U.S. District Judge Robert Shelby ruled that Utah’s constitutional amendment limiting marriage to opposite-sex couples, which voters passed in 2004, violated the U.S. Constitution’s guarantee of equal protection of the laws. His ruling was the first to hold that the Constitution guarantees same-sex couples the right to marry since last summer’s Supreme Court rulings, which took a significant, but limited, step in that direction.

FULL COVERAGE: Gay marriage and the Supreme Court

State officials asked Shelby to put his ruling on hold until an appeals court could review the case, saying it would cause a “chaotic situation.” When Shelby declined to stay his ruling, officials turned to the U.S. 10th Circuit Court of Appeals, which turned them down on Christmas Eve.

The denial by the 10th Circuit panel -- which consisted of two appeals court judges, one appointed by President Obama and the other by President George W. Bush -- was notable because it hinted at skepticism of the state’s arguments. To obtain a stay, the state had to show that it had a substantial likelihood of winning its eventual appeal and that allowing the marriages to continue in the meantime would cause “irreparable harm” to the state’s interests. The judges seemed unconvinced on both counts.

By contrast, when a federal judge struck down California’s Proposition 8, which banned same-sex marriages, the 9th Circuit blocked the ruling and kept the stay in effect until the Supreme Court ruled on the case last June.

Since Shelby’s ruling, hundreds of same-sex couples have wed in Utah -- weddings that in theory could be invalidated if the decision is eventually overturned. As of Monday evening, the Deseret News in Salt Lake City had reported more than 700 marriage licenses had been issued to same-sex couples in the state. Many additional couples married Tuesday.

State officials may face an uphill climb in persuading the Supreme Court to step in at such an early stage. It’s common for the justices to put a ruling on hold once they’ve decided to review a case. But in this case, the state’s appeal hasn’t even been argued to the lower appellate court yet. The justices could simply decline Utah’s request to get involved and wait to see how the lower court handles the matter.

If that happens, same-sex marriages in Utah probably would continue for weeks or months. The appeals court panel that denied the stay Tuesday said the state’s appeal would be expedited. But even in a hurried-up status, an appeals court ruling might not come until early spring.

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Twitter: @DavidLauter

david.lauter@latimes.com