A lawyer defending California’s voter-approved ban on same-sex marriage told a three-judge federal appeals court panel Monday that the ban must be upheld to protect the institution of marriage, which he said is essential for procreation and child rearing.

In a hearing that lasted more than two hours, the panel of judges for the San Francisco-based Ninth Circuit U.S. Court of Appeals fired sharp questions at lawyers backing and opposing Proposition 8, the 2008 ballot measure that repealed the state’s same-sex marriage law.

But two of the three judges appeared to subject the lawyers defending Proposition 8 to greater scrutiny and a stronger challenge of their arguments. That led some legal observers to predict the liberal-leaning court would likely uphold a decision in August by a U.S. District Court judge declaring Prop 8 unconstitutional.

Judge Stephen Reinhardt, an appointee of President Jimmy Carter, is considered one of the court’s strongest liberals and is expected to act favorably toward the two same-sex couples challenging Prop 8 in a case known as Perry v. Schwarzenegger.

Judge Michael Hawkins, a Clinton appointee, is also considered a liberal with a likely favorable leaning toward the gay plaintiffs in the case. The third judge on the panel, N. Randy Smith, was appointed by President George W. Bush and served as chair of the Idaho Republican Party. Legal observers expect him to vote to uphold Prop 8.

Smith is a graduate of Brigham Young University and media reports identified him as a Mormon. The Mormon Church supported the passage of Prop 8 and received criticism from gay activists for encouraging church members to contribute millions of dollars into the Prop 8 election campaign.

Both the plaintiffs in the case — two same-sex couples who are challenging the gay marriage ban — and supporters of Prop 8 have said they would appeal the case to the U.S. Supreme Court if the Ninth Circuit appeals court rules against them. That would bring the question of whether gay marriage is protected by the Constitution before the high court for the first time.

“The key reason that marriage has existed at all in any society and at any time is that sexual relationships between men and women naturally produce children,” said Charles Cooper, one of two attorneys defending Proposition 8 before the appeals court hearing Monday.

Cooper sought to use the procreation element of traditional heterosexual marriage as one of several “rational” reasons why California could ban same-sex marriage without violating the U.S. Constitution.

U.S. District Court Judge Vaughn Walker ruled in August that Proposition 8 violated the federal Constitution’s equal protection and due process clauses, in part, because there was no rational reason to deny marital rights to same-sex couples.

In his arguments, Cooper told the judges that when a relationship between a man and a woman becomes a sexual one, “society immediately has a vital interest in that.” Among other things, “society needs the creation of new life for the next generation,” he said.

Society’s vital interests are also threatened by the possibility of “unintentional and unwanted pregnancy” and single parent households in which children have “poorer outcomes,” he said.

“That sounds like a good argument for prohibiting divorce,” Judge Hawkins said, drawing laughter from the courtroom audience.

“But how does it relate to having two males or two females marry each other and raise children as they can in California and form a family unit where children have a happy, healthy home?” Hawkins asked. “I don’t understand how that argument says we ought to prohibit that.”

Cooper responded by reiterating his procreation argument. “The point and the question is whether or not the State of California has a rational reason for drawing a distinction between same-sex couples who cannot, without the intervention of a third party of the opposite sex, procreate, and opposite-sex couples who … can procreate.”

Theodore Olson, a prominent Republican attorney and constitutional law expert who surprised his GOP colleagues by joining the legal team challenging Proposition 8, strongly disputed claims that same-sex marriage would harm or inhibit procreation or the institution of marriage.

“Same-sex marriage is not going to discourage heterosexual people with heterosexual marriage,” he told the judges Monday. “It is not going to keep them from getting divorced. It is not going to have an effect at all on their choice about having children. On the other hand, the elimination of Proposition 8 cannot possibly hurt the heterosexual relationship at all,” he said.

While Olson argued the merits of why the appeals court should uphold the lower court’s finding that Proposition 8 is unconstitutional, attorney David Boies, a prominent Democrat who teamed up with Olsen in the legal challenge of Prop 8, argued that Prop 8 supporters lacked legal standing to appeal the lower court ruling.

At the time he issued his ruling in August overturning Prop 8 on constitutional grounds, Judge Walker said a decision by California Gov. Arnold Schwarzenegger and the state’s attorney general, Jerry Brown, not to appeal his ruling meant it was unlikely that another party could emerge with legal standing to challenge Walker’s decision.

Walker issued a stay on his own ruling so that the appeals court would have a chance to determine whether the same-sex marriage ban should remain in effect during the appeals process. The Ninth Circuit court extended the stay until it issues its own decision in the case.

But at Monday’s hearing, the judges appeared sympathetic to Boies’ arguments that the conservative political advocacy groups that organized the election campaign for passage of Prop 8 in 2008 did not have legal standing to appeal the lower court ruling.

Boies noted that Prop 8 was a state law in the form of a state constitutional amendment that could only be defended in court at the appeals level by the state or an agent of the state.

A second attorney defending Prop 8 before the Ninth Circuit appeals court Monday argued that a deputy clerk who processes marriage licenses in California’s conservative leaning Imperial County had joined the defense team for the proposition. The attorney, Robert Tyler, told the judges that the deputy clerk was a legitimate representative of the state and thus had legal standing to appeal the case.

But Judge Hawkins appeared to join Boies in expressing strong doubt that the deputy clerk had such standing.

Hawkins and the other appeals court judges said Monday that they would issue a decision on the legal standing matter before they consider the case on its merits. If they determine the Prop 8 supporters and their legal team don’t have standing, they will send the case back to Judge Walker, who likely would order state officials to cease enforcing Prop 8.

However, Prop 8 backers would then be expected to immediately appeal the case to the U.S. Supreme Court and ask the high court to reinstate a stay to keep Prop 8 on the books until the Supreme Court issues its own decision in the case.

“I think the arguments made even clearer to all of us that the judges are wrestling with whether this litigation even can continue with the only party seeking to appeal being those who do not appear to have legally recognizable interests in this case,” said Jennifer Pizer, an attorney with Lambda Legal.

“So I would not be at all surprised if they decide that the appeal should not proceed” based on a lack of legal standing, Pizer said.

Meanwhile, one of the leading groups supporting Prop 8 issued a statement Monday denouncing Ninth Circuit Judge Reinhardt for refusing to recuse himself from the case because his wife is a prominent attorney with the ACLU who has worked to oppose Prop 8.

“This hearing makes a mockery of the federal judiciary,” said Brian Brown, president of the National Organization for Marriage. “Citizens are entitled to a guarantee of impartiality from their judiciary,” he said. “Yet here we have the spectacle of a federal appeals court justice ruling on a case in which his wife represents a group that is a participant.”

Reinhardt issued his own statement last month saying his wife’s views on the case would not detract from his ability to be fair and impartial in his ruling on the case.