SAN FRANCISCO (AP) – Proponents of same-sex marriage told a judge that arguments over whether marriage is designed to foster procreation and whether gays and lesbians make good parents are irrelevant to their case.

Twelve couples are suing to get California to overturn its statutory ban on same-sex marriage, a response to legal claims from two Christian groups.

In briefs filed Dec. 3, the couples’ lawyers pointed out to Superior Court Judge Richard Kramer that California’s Legislature and Supreme Court have already settled the procreation-parenting question by allowing gays and lesbians to have children through adoption or reproductive technology.

“California’s public policy unambiguously rejects the notion that families headed by same-sex couples provide a harmful or inferior environment for children, and unambiguously has embraced the premise that same-sex couples and their children should be treated equally,” they wrote.

Kramer has set a Dec. 22 hearing on the constitutional issues raised in the couples’ lawsuit and a companion case brought by the city of San Francisco. Both suits claim a 1977 state law that defines marriage as a union between a man and a woman is unconstitutional because California’s equal protection clause bars discrimination.

Attorney General Bill Lockyer has told the court that limiting marriage to opposite-sex couples does not run afoul of the California Constitution because that “common and traditional understanding” of matrimony “predates the founding of this state or nation.” Lockyer said it was up to voters or the Legislature to decide whether to change that.

The Christian groups, the Arizona-based Alliance Defense Fund and the Campaign for California Families, adopted Lockyer’s reasoning and took it a step further, arguing that the state should maintain the status quo because “children do best with both a mother and a father.”

The couples, who are represented by lawyers from the National Center for Lesbian Rights, the American Civil Liberties Union and Lambda Legal, said the groups’ claim amounts to gender discrimination.

In court papers, the San Francisco City Attorney’s office also rejected the “procreation and childrearing rationale” for not allowing same-sex couples to wed.

“Marriage in this state has never been limited in any other way that suggests that its major or primary purpose is in fact procreation,” the city’s lawyers said. “On the contrary, a 90-year-old heterosexual may legally marry, a heterosexual stricken with a fatal illness and on his or her deathbed may legally marry, a heterosexual person who is imprisoned for life without parole may legally marry.”

They also urged Kramer to prohibit the opponents from presenting any evidence on the viability of families headed by gay and lesbian parents without giving them a chance to offer counter-evidence.

Both sides have vowed to appeal the cases to the California Supreme Court.