In a bold political and legal move, the Obama administration formally expressed its support for same-sex marriage in California, setting up a high stakes political and constitutional showdown at the U.S. Supreme Court over a fast-evolving and contentious issue.

In a broadly worded legal brief on Thursday that senior government sources said had President Barack Obama's personal input and blessing, the Justice Department asserted gay and lesbian couples in the nation's most populous state have the same "equal protection" right to wed and that voters there were not empowered to ban it.

"Use of a voter initiative to promote democratic self-governance cannot save a law like Proposition 8 that would otherwise violate equal protection," said the brief. "Prejudice may not however be the basis for differential treatment under the law."

California's 2008 Proposition 8 referendum revoked the right of same-sex couples to wed after lawmakers and the state courts previously allowed it.

While the administration weighed in on the situation in California, it specifically refused to argue the constitutional right for same-sex couples to wed there should be extended to the 41 states that currently define marriage as between one man and one woman.

The justices will hear the case in March.

"The government seeks to vindicate the defining constitutional ideal of equal treatment under the law," said Attorney General Eric Holder. "Throughout history, we have seen the unjust consequences of decisions and policies rooted in discrimination."

"The issues before the Supreme Court in this case and the Defense of Marriage Act case are not just important to the tens of thousands Americans who are being denied equal benefits and rights under our laws, but to our nation as a whole," Holder added.

The White House was not expected to issue a separate statement.

The California matter and another appeal over the federal Defense of Marriage Act will produce blockbuster rulings from the justices in coming months.