SAN FRANCISCO - Justices of the California Supreme Court on Wednesday announced they would agree to hear arguments as to why they should strike down Prop. 8, the recently enacted ballot measure that bans gay marriage in the state.

In their order, the high court said that parties involved must prepare arguments and brief answering these three questions:

--Is Prop. 8 invalid because it constitutes a revision of, rather than an amendment to the California Constitution?

--Does Prop. 8 violate the separation of powers doctrine under the California Constitution?

--If Prop. 8 is not unconstitutional, what is the effect, if any, on the marriages of same-sex couples performed before the adoption of Prop. 8?

The court also denied a request by the petitioners - a large group of cities, counties, churches and civil and gay rights organizations to stay or stop the enactment of the measure, meaning that until they issue a ruling the state must continue to disregard same-sex marriages.

San Francisco Mayor Gavin Newsom praised the court's decision.

"I applaud the Supreme Court's decision to review this important civil rights issue. Every Californian deserves equal protection under the law. I am optimistic that the Supreme Court will affirm that separate is not equal," Newsom said.

Rick Jacobs, founder and chairman of the Courage Campaign, an online progressive issues organization, said Wednesday that his organization will proceed with an ambitious online petition gathering effort to qualify a 2010 ballot measure to reverse Prop. 8.

"While we are confident the court will find in favor of protecting marriage rights for all, we are preparing for any outcome. Our sincere hope is any action the court takes does not negatively affect the thousands of couples who chose to get married before the November election.

"As we await the court's decision, we will work to engage every community in California by mobilizing our members in a grassroots effort to restore marriage rights," Jacobs said in a statement

Meanwhile, Yes on 8/ProtectMarriage.com officials said they too were pleased by the high court's decision.

"This is a great day for the rule of law and the voters of California," said ProtectMarriage.com General Counsel Andy Pugno. "This order means that voters will get their day in court and ensures that voters will have a vigorous defense of Prop. 8 before the California Supreme Court. We are profoundly gratified with the court's order and are confident that Prop. 8 will be upheld."

The petitioners argue that Prop. 8 represents an improper revision rather than an amendment of the California Constitution. To legally revise the constitution requires a three-fourths vote of the state legislature or by convening a state constitutional convention. Constitutional revisions, opponents argue, cannot be made via the ballot box.

Six justices - Chief Justice Ronald M. George, Justice Marvin R. Baxter, Justice Kathryn M. Werdegar, Justice Ming W. Chin, Justice Carlos R. Moreno, and Justice Carol A. Corrigan - signed the court's order, although Justice Moreno indicated that he would grant the requests to stay the operation of Prop. 8 pending the court's resolution of these matters.

Justice Joyce L. Kennard would deny these petitions without prejudice to the filing in the Supreme Court of an appropriate action to determine Proposition 8's effect, if any, on the marriages of same-sex couples performed before Proposition 8's adoption.

In its order, the court said that it would expedite hearing the matter, saying that initial briefs must be filed before Dec. 19 and that oral arguments could be scheduled as early as March 2009.