SAN FRANCISCO (AP) — A state senator and a conservative family group are pursuing legal action to block a law that would grant same sex couples in California the same legal rights and responsibilities as married spouses.

Three months after Gov. Gray Davis signed the groundbreaking bill, a Superior Court judge in Sacramento on Thursday denied the state’s motions to have the cases thrown out.

Judge Thomas M. Cecil ruled that Sen. William “Pete” Knight and the Campaign for California Families had a valid claim in arguing that the law would undermine a 2000 ballot measure defining marriage as a union between a man and a woman.

“Having our day in court is a victory for the 4.6 million California voters who demanded that marriage be protected,” said Randy Thomasson, executive director of Campaign for California Families.

At the same time, attorneys for the state’s largest gay lobbying group and a dozen gay and lesbian couples who signed on to the suits also declared victory after the Judge Cecil’s ruling. The judge rejected the plaintiff’s request for a preliminary injunction that would have blocked the state from notifying thousands of same-sex couples already registered as domestic partners about the law, which is scheduled to take effect on Jan. 1, 2005.

The plaintiffs did not demonstrate “that it is reasonably probable that they shall succeed upon the merits of their action” to restrain the state at this point, the judge wrote.

The new law was hailed upon its passage as offering the most generous protections to gays and lesbians outside Vermont. It expands the rights of gay couples in areas ranging from health coverage and parental status to property ownership and funeral arrangements. It gives both partners equal status as parents if they have or adopt a child together, and allow them to seek child support and alimony.

Mathew Staver, who is representing Thomasson’s group for the Florida-based Liberty Counsel, said Friday that neither side disputes the facts of the case. At issue is a legal dispute over whether the domestic partners bill Davis signed in September, as well as companion legislation enacted two years earlier, “creates a parallel to marriage for same-sex couples” that violates Proposition 22, the marriage-protection measure.

“You can name a bill anything you want to,” Staver said. “What is really at issue is not the name of it, but what the bill does.”

But David Codell, a lawyer representing the gay-rights group Equality California, argued that the opponents of the domestic partnership bill are the ones attempting a “bait-and-switch.”

Noting that Proposition 22 appeared on the March 2000 ballot the year after California created its domestic partner registry, Codell said that official arguments that were mailed before the election “specifically told the voters that Proposition 22 wasn’t going to take away anyone else’s rights.” He said the plaintiffs are trying to inject the initiative with meaning it never had.

“It is simply not the case that married couples have the monopoly on the rights and protections that come with marriage,” Codell said.

Staver said he plans to file a motion for an expedited hearing after the holidays, which would bring the case back to Cecil’s courtroom in mid-March. Gov. Arnold Schwarzenegger, whose administration is now a defendant in the case he inherited from Davis, has not yet taken a position on the domestic partner legislation.

Sen. Knight (R-Palmdale) originally sought permission from the Secretary of State to gather signatures for a ballot initiative to overturn the new law. But on Friday his spokesman said Knight has decided to pursue the case through the courts rather than through the voters.

According to Equality California, since no signatures were submitted by the Dec. 21 deadline, the proposed referendum has failed to qualify for the California ballot.