The Obama administration filed court papers Monday claiming the 1996 Defense of Marriage Act discriminates against gay and lesbians. But in a move that has angered gay rights activists, the Justice Department urged dismissal of a lawsuit challenging the act, noting it remains law until Congress repeals it. Opponents of same-sex marriage accused the White House of insincerity in its defense of the act, and supporters demanded a more proactive approach to ensuring that all citizens enjoy equal protection under the law.