Utah state attorneys filed their opening argument to the federal appeals court reviewing the state's same-sex marriage ban, saying the optimal environment for raising children is with a mother and father.

The voluminous brief, filed late Monday ahead of a midnight deadline, is the first step in a process that will lead to an April 10 hearing before the Denver-based 10th U.S. Circuit Court of Appeals.

The court will then decide if it agrees with a federal judge in Utah who in mid-December overturned the 2004-voter passed ban saying it violates gay and lesbian couples' rights to due process and equal protection under the 14th Amendment. The appeals court also is reviewing a similar decision about Oklahoma's ban.

Attorneys for three gay and lesbian couples who sued Utah have until Feb. 25 to respond.

The state contends redefining marriage poses "real, concrete risks to children" because not having a mother or father leads to emotional damage. The state said its duty is to look out for the long-term interests of children who can't defend themselves. The state also believes allowing same-sex marriages would lead to reduced birth rates, which would bring demographic and economic crisis.

"The diversity of having both a mom and a dad is the ideal parenting environment," wrote Gene Schaerr, an outside attorney who has been hired by the state to defend the law. "That model is not intended to demean other family structures, any more than giving an A to some students demeans others."

The state made similar arguments in court papers filed before the U.S. Supreme Court in early January when it asked the justices to halt gay marriages that were occurring in Utah. The high court approved the request, granting an emergency stay while the 10th Circuit considers the case.

Attorneys representing three gay and lesbian Utah couples scoffed at the notion that gay and lesbian couples make inferior parents, saying the state provides no scientific evidence to back its claim.

Shannon Minter, legal director for the National Center for Lesbian Rights, said Tuesday the state's brief offers no justification for harming sex-sex couples and their families.

"The law should support all families, not make it harder for some families to take care of themselves and their children," Minter said in an emailed statement. "Our Constitution does not tolerate laws that single out a group of people in order to treat them unequally."

More than 1,000 gay couples married in Utah before the Supreme Court granted the stay last month. Utah Gov. Gary Herbert has instructed state agencies to stop granting benefits to the couples, save for allowing them to jointly file taxes.

U.S. Attorney General Eric Holder, meanwhile, said the federal government will recognize the marriages and grant corresponding benefits.

Utah state attorneys believe the appeals court ultimately will decide the validity of the marriages, but gay rights attorneys think the marriages should remain valid no matter what the court decides.

Utah's gay marriage ban was passed by 66 percent of voters in 2004. In the brief, the state says U.S. District Judge Robert J. Shelby did not give "proper deference to the choice of Utah's citizens" when he struck down the ban in a surprise Dec. 20 ruling.