The U.S. Supreme Court, acting on an appeal from conservative defenders of California’s ban on same-sex marriage, overruled a federal judge in San Francisco today and blocked video coverage of the trial on YouTube.

In a brief order, the justices said they were halting the move by U.S. District Judge Vaughn Walker “permitting real-time streaming” of the trial, “except as it permits streaming to other rooms within the confines of the courthouse in which the trial is to be held.”

“Any additional order permitting broadcast of the proceedings is also stayed pending further order of this court,” the justices said. They added that the temporary order “will remain in effect until Wednesday, Jan. 13.”

The high court did not explain its reasoning.

Only Justice Stephen G. Breyer, a San Francisco native, dissented. “In my view, the court’s standard for granting a stay is not met” in this case, he wrote. “In particular, the papers filed, in my view, do not show a likelihood of ‘irreparable harm.’ ”

Under the court’s rules, lawyers can seek an emergency order only if they can show their clients will suffer “irreparable harm” if the justices fail to act. In this case, the defenders of Prop. 8 said their witnesses could be subjected to harassment and intimidation if they testified in favor of the ban on marriage for gay and lesbian couples.

On Sunday, the attorneys challenging Prop. 8 urged the court to turn down the appeal and to allow video coverage. They said millions of Californians and others are interested in the proceedings and the public had a right to know what was taking place in its courtrooms.

Recently, the U.S. 9th Circuit Court of Appeals allowed some TV coverage of civil trials. And based on that move, Judge Walker decided to allow YouTube to post video after each day’s proceedings.

This is the second time in recent months in which the high court has intervened on behalf of the defenders of “traditional marriage” and granted an emergency appeal.

In October, the justices blocked officials in the state of Washington from releasing the names of 138,000 people who signed ballot petitions seeking to overturn a state law giving equal benefits to gay and lesbian couples. Under Washington law, the names were considered public record.

But attorney James Bopp told the high court that the signers of these petitions could be subjected to harassment if their names were revealed. And the court granted an order blocking the release.

david.savage@latimes.com