The lawyers defending California’s Proposition 8 and its ban on same-sex marriage urged the U.S. Supreme Court today to block video coverage of next week’s trial in San Francisco.

They filed an emergency appeal with Justice Anthony M. Kennedy and argued that their client’s right to a fair trial would be jeopardized if each day’s proceedings were put on YouTube.

The trial “has the potential to become a media circus,” wrote attorney Charles Cooper. “The record is already replete with evidence showing that any publicizing of support for Prop. 8 has inevitably led to harassment, economic reprisal, threats, and even physical violence. In this atmosphere, witnesses are understandably quite distressed at the prospect of their testimony being broadcast worldwide on YouTube.”

FOR THE RECORD: An earlier version of this article said opponents of Proposition 8 sent petitions signed by more than 50,000 people urging TV coverage of the trial. More than 140,000 names were sent on Friday.

Kennedy asked for a response from the state by noon on Sunday.

At issue is whether the California voter initiative that forbids the state from granting marriage licenses to gay and lesbian couples violated the Constitution’s guarantee of equal protection of the laws.

U.S. District Judge Vaughn Walker, who is conducting the trial beginning on Monday, agreed to limited TV coverage. The proceedings will be taped and made available to YouTube at the end of the day. He acted based on a recent rule change by the U.S. 9th Circuit Court of Appeals allowing TV coverage of some civil cases.

On Friday, opponents of Prop. 8 sent petitions signed by more than 140,000 people urging TV coverage of the trial.

“It’s vital that this trial be open to the public,” said Rick Jacobs, founder of the Courage Campaign Institute in Los Angeles. “The outcome will affect millions of people, and it’s the American way to open the judicial process to the public.”

Foes of Prop. 8 criticized the appeal to the Supreme Court as a desperate attempt “to shut cameras out.”

“Those who want to ban gay marriage spent millions of dollars to reach the public with misleading ads, rallies and news conferences during the campaign to pass Prop. 8. We are curious why they now fear the publicity they once craved,” said Chad Griffin, Board President of the American Foundation for Equal Rights.

“Apparently transparency is their enemy, but the people deserve to know exactly what it is they have to hide.”

david.savage@latimes.com