Attorney General Eric H. Holder Jr. sent a letter to Congress on Wednesday saying that the Justice Department will now take the position in court that the act should be struck down as a violation of same-sex couples' rights to equal protection under the law.

"The president and I have concluded that classifications based on sexual orientation warrant heightened scrutiny and that, as applied to same-sex couples legally married under state law," a crucial provision of the act is unconstitutional, Mr. Holder wrote.