SAN FRANCISCO – California's highest court agreed Wednesday to hear several legal challenges to the state's new ban on same-sex marriage but refused to allow gay couples to resume marrying before it rules.

The California Supreme Court accepted three lawsuits seeking to nullify Proposition 8, a voter-approved constitutional amendment that overruled the court's decision in May that legalized gay marriage.

All three cases claim the measure abridges the civil rights of a vulnerable minority group. They argue that voters alone did not have the authority to enact such a significant constitutional change.

As is its custom when it takes up cases, the court elaborated little. However, the justices did say they want to address what effect, if any, a ruling upholding the amendment would have on the estimated 18,000 same-sex marriages that were sanctioned in California before election day.

Gay rights groups and local governments petitioning to overturn the ban were joined by the measure's sponsors and Attorney General Jerry Brown in urging the Supreme Court to consider whether Proposition 8 passes legal muster.

The initiative's opponents had also asked the court to grant a stay of the measure, which would have allowed gay marriages to begin again while the justices considered the cases. The court denied that request.

The justices directed Brown and lawyers for the Yes on 8 campaign to submit arguments by Dec. 19 on why the ballot initiative should not be nullified. It said lawyers for the plaintiffs, who include same-sex couples who did not wed before the election, must respond before Jan. 5.

Oral arguments could be scheduled as early as March, according to court spokeswoman Lynn Holton.

Both opponents and supporters of Proposition 8 expressed confidence Wednesday that their arguments would prevail.

But they also agreed that the cases present the court's seven justices — six of whom voted to review the challenges — with complex questions that have few precedents in state case law.

The lawsuits argue that voters improperly abrogated the judiciary's authority by stripping same-sex couples of the right to wed after the high court earlier ruled it was discriminatory to prohibit gay men and lesbians from marrying.

"If given effect, Proposition 8 would work a dramatic, substantive change to our Constitution's 'underlying principles' of individual on a scale and scope never previously condoned by this court," lawyers for the same-sex couples stated in their petition.

The measure represents such a sweeping change that it constitutes a constitutional revision as opposed to an amendment, the documents say. The distinction would have required the ban's backers to obtain approval from two-thirds of both houses of the California Legislature before submitting it to voters.

Over the past century, the California Supreme Court has heard nine cases challenging legislative acts or ballot initiatives as improper revisions. The court eventually invalidated three of the measures, according to the gay rights group Lambda Lega.