"The trial court's ruling in Utah goes further than the court has gone so far, and so it is not surprising that the justices — without comment or dissent — put that ruling on hold, pending further review," said Notre Dame law professor Richard Garnett. He noted that the court often gave states the benefit of the doubt when they appealed.

Lawyers for the American Civil Liberties Union were disappointed but said the court's action should not affect gay couples who lawfully married in Utah.

"Though future marriages are on hold for now, the state should recognize as valid those marriages that have already been issued," said John Mejia, legal director for the ACLU of Utah.

A similar issue arose in California in 2008 after the state Supreme Court ruled that gays and lesbians could marry. The same-sex marriages that ensued were upheld as valid, even though voters passed Proposition 8 within months, restoring a state ban on gay marriages.

But in Utah, the federal judge's ruling is not a final decision because it is still under appeal, so the question of validity is less clear.

Opponents of gay marriage welcomed the high court's intervention.

"It was outrageous that this brazen judge appointed by President Obama would substitute this view for the sovereign decision by both the Utah Legislature and the people of the state, who voted overwhelmingly in favor of defining marriage as the union of one man and one woman," said Brian Brown, president of the National Organization for Marriage.

Shelby was recommended for the bench by Utah's two Republican senators, Orrin G. Hatch and Mike Lee.