A federal court overturned a California initiative outlawing same-sex marriage on Wednesday, raising the stakes in one of the highest-profile gay-rights battles in the country.

U.S. District Court Judge Vaughn Walker found that the ban on gay marriage violated due process and equal protection as guaranteed under the Constitution. The decision invalidates a 2008 vote in which 52 percent of California voters supported outlawing same-sex marriage in a ballot initiative known as Proposition 8.

“Moral disapproval alone is an improper basis on which to deny rights to gay men and lesbians,” Walker concluded. “The evidence shows conclusively that Proposition 8 enacts, without a reason, a private moral view that same-sex couples are inferior to opposite-sex couples.”

The law, Walker wrote, “does nothing more than enshrine in the California Constitution the notion that opposite-sex couples are superior to same-sex couples.”

Supporters of Prop 8 have indicated they will appeal the decision to the 9th Circuit Court of Appeals, a relatively liberal court, but the battle could extend all the way to the Supreme Court.

The decision is expected to elevate the issue of gay rights in the 2010 battle for control of Congress, and in California could play out in the fight between Democratic incumbent Sen. Barbara BoxerBarbara Levy BoxerHispanic civil rights icon endorses Harris for president California AG Becerra included in Bloomberg 50 list Climate debate comes full circle MORE (D-Calif.) and Republican Carly Fiorina, the former Hewlett-Packard CEO.

Conservative groups immediately blasted the decision and expressed confidence that the Supreme Court would eventually rule in their favor.

“With a stroke of his pen, Judge Walker has overruled the votes and values of 7 million Californians who voted for marriage as one man and one woman,” said Brian Brown, president of the National Organization for Marriage (NOM).

“[L]et’s not lose sight of the fact that this case is headed for the U.S. Supreme Court, where the right of states to define marriage as being between one man and one woman will be affirmed,” Brown added.

Gov. Arnold Schwarzenegger (R), meanwhile, praised the decision.

“For the hundreds of thousands of Californians in gay and lesbian households who are managing their day-to-day lives, this decision affirms the full legal protections and safeguards I believe everyone deserves,” he said in a statement.

Walker was initially nominated by President Reagan, and re-nominated by President George H.W. Bush after his confirmation was held up in the Senate.

Brown suggested that Walker was biased due to being gay himself.

“Here we have an openly gay … federal judge substituting his views for those of the American people and of our Founding Fathers,” Brown said.

But Walker was not always seen as a pro-gay justice. When first nominated in 1987, a coalition of Democrats including Rep. Nancy Pelosi (D-Calif.) opposed his nomination, accusing him of “insensitivity” to gays.

The California Supreme Court effectively legalized gay marriage earlier in 2008 by overturning a voter-approved ban that was passed in 2000. Prop 8 superseded that decision by amending the state’s constitution.

Opponents of the law asked the state Supreme Court earlier this year to overturn the initiative on procedural grounds, but were rebuffed.