SAN FRANCISCO (AP) – Opponents of same-sex marriage told a California judge that same-sex unions are contrary to the purpose of marriage itself: procreation.

Robert Tyler, an attorney with the Alliance Defense Fund, an Arizona-based Christian law firm who is fighting San Francisco’s lawsuit trying to legalize same-sex marriages in California, also said that same-sex marriages are not ideal institutions to raise children, either.

In an interview, he said, “clearly, the best environment for children” is a marriage between a man and woman. A same-sex marriage, he said, would deprive a child of either a mother or father.

The ADF arguments were submitted to Superior Court Judge Richard Kramer in a case brought by San Francisco, and same-sex couples denied marriage licenses. They sued in state court here, claiming the California Constitution’s equal protection clause permits same-sex marriage, despite a state law defining it as between opposite sexes.

San Francisco Mayor Gavin Newsom and same-sex couples sued after the California Supreme Court said Newsom overstepped his authority when he issued about 4,000 same-sex marriage licenses earlier this year. The state Supreme Court nullified those marriages as well.

Newsom’s actions and Massachusetts’ highest court interpreting that state’s constitution to permit same-sex marriages prompted a nationwide same-sex marriage backlash.

Voters passed constitutional amendments in all 11 states where they were on the ballot Nov. 2. Proponents of those measures espoused similar arguments that ADF submitted in state court here.

Defending the 1977 California state law defining marriage between a man and woman, Attorney General Bill Lockyer has told the court that laws limiting marriage do not run afoul of California’s Constitution.

Portending that Judge Kramer, or even the California Supreme Court, won’t have the final say on the issue, Lockyer said it was up to voters or the Legislature to decide whether to change “the common and traditional understanding” of matrimony that “pre-dates the founding of this state or nation.”

In court papers, Lockyer also took pains to point out that his office rejected many of the arguments that opponents of same-sex marriage are making, such as that “same-sex relationships are less committed or stable than opposite-sex relationships.”

Tyler said there is “discussion within the ranks” about whether to put an initiative before California voters banning same-sex marriages.

“Societies have long recognized that one of the purposes of marriage is to encourage procreation within the marital union. That’s the primary and fundamental purpose of marriage,” Tyler said.

Judge Kramer has set a Dec. 22 hearing. Kramer is not expected to immediately rule.

But whatever his decision, all sides agree it would be appealed.