Clerk Chuck Storey, who took office in January, argued in a brief submitted to the 9th U.S. Circuit Court of Appeals that his participation is "appropriate and necessary" to enable the court to decide the constitutionality of the voter initiative.
The backers of Proposition 8 are seeking to appeal U.S. District Judge Vaughn Walker's ruling last year that the measure passed by state voters in 2008 violates the U.S. Constitution.
But the appeals court has expressed doubts as to whether the measure's sponsors have the legal right under federal law to appeal in light of the fact that Gov. Jerry Brown and Attorney General Kamala Harris have declined to do so.
The federal court has asked the California Supreme Court to decide whether the state law would allow the sponsors to appeal, and it could take the state high court at least several months to issue a decision on that issue.
Meanwhile, Storey, who says his duties will be affected by whether gay marriage is legal, is seeking to step in as an official party to defend Proposition 8 in the appeal.
The clerk said in a statement Friday, "I took an oath of office to uphold the California Constitution, and Proposition 8 is part of the Constitution."
A spokesman for two same-sex couples who challenged the ban with a civil rights lawsuit was not immediately available for comment.
Imperial County previously sought to join the case through a deputy county clerk, but the federal appeals court said in January that a deputy clerk didn't have the standing, or authority, to be a party in the case.
The appeals court said, however, that a request by a county clerk, rather than a deputy, "might have merit," but did not decide the issue.
The appeals panel has no deadline for acting on Storey's request.
Storey is represented by lawyers from Riverside County-based Advocates for Faith & Freedom, a nonprofit legal group.
The group's general counsel, Robert Tyler, said, "We believe we have a government defendant who has a sufficient and compelling interest in defending Proposition 8."