The randomly selected judges of the 9th U.S. Circuit Court of Appeals are a liberal, Stephen Reinhardt, of Los Angeles; a moderate, Michael Hawkins, of Arizona; and a conservative, Randy Smith, of Idaho.
They will hold a two-hour hearing in San Francisco next Monday on an appeal by Proposition 8 sponsors of a trial court ruling that struck down the voter initiative.
Proposition 8, enacted by California voters in 2008, restricts marriage to the union of a man and a woman.
In August, U.S. District Judge Vaughn Walker ruled that the measure violates the U.S. Constitution's guarantees of equal treatment and due process.
His ruling has been stayed during the appeal.
The sponsors of Proposition 8 and their committee, Protect Marriage, contend the measure is valid because it is based on a rational goal of encouraging responsible child-rearing by biological parents within a marriage.
The eventual ruling by the three-judge panel will not be the end of the line for the case. The panel's decision can be appealed to a larger 11-judge panel of the 9th Circuit and then to the U.S. Supreme Court.
Reinhardt, 79, one of the most liberal members of the court, will be the senior member of the three-judge panel. A former private lawyer, he was appointed to the appeals court by President Jimmy Carter and took office in 1980.
Hawkins, 65, may provide the swing vote in the case. He is a former U.S. attorney in Arizona and former private lawyer and was appointed in 1994 by President Bill Clinton.
Smith, 61, a former state court judge in Idaho, was appointed by President George W. Bush in 2007.
Hawkins told an Internet legal blog in 2003 that he thinks of himself as being "entirely moderate in all things."
He said, "My judicial philosophy is really pretty simple: people involved in the legal process should be treated fairly and judges should decide cases on the merits."
Reinhardt told the same legal blog in 2004 that liberal judges "do not manipulate the law to receive a predetermined result" and said judges should not consider likely public reactions to their decisions.
"We are required to resolve cases and controversies properly brought before us in accordance with the Constitution, relevant statutes, and precedents," Reinhardt said.