Reporting from San Francisco - A federal judge refused Wednesday to dismiss a constitutional challenge to Proposition 8, ruling that a trial was required to resolve legal and factual disputes over the voter-approved ban on same-sex marriage.

U.S. District Judge Vaughn R. Walker, ruling after nearly two hours of argument in San Francisco, rejected arguments by Proposition 8 proponents that precedent and tradition clearly showed last November's ballot measure was permissible under the U.S. Constitution.

Walker's decision means the case will proceed to trial as scheduled in January, unless appeals delay it.

The California Supreme Court ruled in May that Proposition 8, passed by 52.3% of voters, did not violate the state Constitution. The suit before Walker says the measure violates the federal Constitution's guarantees of equal protection and due process.

During the hearing, Charles Cooper, representing the Proposition 8 campaign, argued that marriage historically has been reserved for unions between a man and a woman because only opposite-sex couples can procreate "naturally."

Walker, however, noted that not all married couples can procreate.

"Just last month," Walker said, "I performed a wedding in which the groom was 95 and the bride was 83. I did not demand that they prove they would engage in procreation."

Proposition 8 backers also argued that precedent required Walker to uphold the measure as constitutional. They cited a 1972 case involving a Minnesota law that limited marriage to unions between a man and a woman.

The Minnesota Supreme Court had rejected an equal protection challenge of that law, and the U.S. Supreme Court, without issuing a full-blown opinion, declined to hear an appeal.

"We can't put much stock in that case, can we?" Walker told the lawyers. He described the case as "old," "very limited" and "not a considered decision of the Supreme Court."