LAS VEGAS — A federal court challenge to Nevada’s ban on same sex marriage has been turned back in U.S. District Court, but proponents vowed Friday to fight on with an argument that a pair of state laws regarding same-sex unions unconstitutionally make gay couples “second-class citizens.” Lambda Legal Defense and Education Fund attorney Tara Borelli noted that a Thursday ruling by U.S. District Chief Judge Robert Jones came a day before the U.S. Supreme Court considered whether to take up the gay marriage question, and just weeks after voters approved same-sex marriage in three states and defeated a ban in a fourth.“We think this decision is not only out of step with where the country is headed, but also completely wrong on the law,” Borelli said. She said a challenge will be filed with the 9th U.S. Circuit Court of Appeals in San Francisco.Jones, in Reno, ruled that Nevada has “a legitimate state interest” in maintaining the traditional institution of marriage and that excluding the recognition of same-sex couples is “rationally related to furthering that interest.” The question “is not the wisdom of providing for or recognizing same-sex marriages as a matter of policy,” Jones wrote in his 41-page order. Rather, he called it a constitutional question about Nevada’s right to prohibit recognition of marriages from other states “if those laws do not conform to Nevada’s one-man-one-woman civil marriage institution.”Monte Stewart, lawyer for the Coalition for the Protection of Marriage, a Boise, Idaho-based advocacy group that opposes gay marriage and was involved in the case, declined comment. Officials with Gov. Brian Sandoval’s office, Nevada state attorney general’s office and Carson City attorney’s office declined to comment.The Nevada lawsuit, Sevcik v. Sandoval, was filed in April on behalf of eight Nevada couples. It was the first by Lambda Legal to make the direct state marriage equality claim in federal court. It said the 2002 state constitutional amendment prohibiting same-sex marriage violated the Equal Protection Clause of the U.S. Constitution by denying same-sex couples in Nevada the same rights, dignity and security that other married couples enjoy.Borelli said letting domestic partners register their legal status but not marry “brands these loving couples and their children as second-class citizens.”The lawsuit also accused the state of establishing a “selective bar to access to marriage” with a 2009 domestic partnership law that passed over a veto by then-Gov. Jim Gibbons, a Republican. And it maintained that same-sex couples are still discriminated against by hospital officials and police officers who question their relationship status because they aren’t legally recognized as spouses.The case in Nevada followed a four-year legal battle in California over that state’s Proposition 8 ban on same-sex marriages — one of the questions now on the doorstep of the U.S. Supreme Court. Justices are considering taking up a challenge to part of the federal Defense of Marriage Act of 1996.During a hearing in Las Vegas in May, Jones noted a difference in the California and Nevada cases. The California ballot initiative aimed to kill a law that had been enacted to recognize same-sex marriages, while the Nevada Legislature didn’t extend to same-sex couples the same degree of legal protection.