WASHINGTON — The Obama administration is quietly considering urging the Supreme Court to overturn California’s ban on gay marriage, a step that would mark a political victory for advocates of same-sex unions and a deepening commitment by President Barack Obama to rights for gay couples. Obama raised expectations among opponents of the Proposition 8 ban when he declared in last month’s inaugural address that gays and lesbians must be “treated like anyone else under the law.” The administration has until Feb. 28 to intervene in the case by filing a “friend of the court” brief. The Proposition 8 ballot initiative …