The Obama administration has abandoned its defense of a portion of a federal law that limits the definition of marriage to the union between a man and woman.

The announcement yesterday came as the administration faced March 11 deadlines to file motions to dismiss New York and Connecticut challenges to the law.

Attorney General Eric H. Holder Jr. said that he had written to House Speaker John A. Boehner that the administration could no longer defend in court the constitutionality of Section 3 of the 1996 Defense of Marriage Act. (Read the Holder Letter.)

Section 3 provides that in interpreting any act of Congress or action of a federal government agency, the word “marriage” means only a union between one man and one woman. This has the effect of denying to same-sex couples, even in states where their marriages are legally recognized, government benefits that are available to men and women in heterosexual unions.

“[T]he 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, Section 3 of DOMA is unconstitutional,” Mr. Holder wrote.

If it chooses to defend the law, Congress will now have to hire its own lawyers. But the administration’s stance will give added ammunition to opponents of the law.

Mr. Holder wrote to Mr. Boehner that the record of justifications offered by Congress for Section 3 “contains numerous expressions reflecting moral disapproval of gays and lesbians and their intimate and family relationships—precisely the kind of stereotype-based thinking and animus the Equal Protection Clause is designed to guard against.”

The administration will continue to enforce the law as it is obliged to do, he said, “unless and until” Congress repeals it or the courts find it unconstitutional, but it would no longer argue its constitutionality in court.

Mr. Holder said the decision was the result of a re-examination prompted by cases filed in November in two courts of the Second Circuit; Windsor v. United States, 10- cv- 8435 (S.D.N.Y.), and Pedersen v. OPM, 10-cv-1750 (D.Conn.) (NYLJ, Nov. 12, 2010)

In Windsor, which is before Southern District Judge Barbara Jones, plaintiff Edith Schlain Windsor sued seeking a refund of $350,000 in estate taxes she had to pay because of the death of her companion of 44 years, Thea Clara Spyer. Ms. Windsor, now 81, ultimately married Ms. Spyer in Canada, a marriage recognized by New York state.

Roberta A. Kaplan of Paul, Weiss, Rifkind, Wharton & Garrison, one of the attorneys representing Ms. Windsor, was elated by the announcement.

“We’re extremely pleased that the president and the Department of Justice have now recognized what we initially asserted when we filed the case—there was no way to justify the fact that our client had to pay a $350,000 estate tax bill simply because she was married to a woman,” Ms. Kaplan said. “We said the government would have a very hard time justifying the disparate treatment and it turns out we were right—there really is no way to justify it.”

Ms. Windsor, in a statement issued by the American Civil Liberties Union, which is also representing her, congratulated President Barack Obama and the Justice Department for “doing the right thing.”

“My only regret is that my beloved late spouse, Thea Spyer, isn’t here today to share in this historic moment,” Ms. Windsor said. “But in my heart, I feel that she knows.”

In Pedersen, which is before Connecticut District Judge Vanessa Bryant, seven gay and lesbian plaintiffs who are legally married, or were until being widowed, claim that the Defense of Marriage Act (DOMA) violates the Constitution because it refuses to recognize lawful marriages for purposes of laws governing defined benefit pension plans and state retirement plans, laws governing benefits for federal retirees, the Family Medical Leave Act, the Internal Revenue Code and the Social Security laws.

Stricter Standard

Before Pedersen and Windsor, Mr. Holder said, the Justice Department had defended §3 of DOMA “classifications based on sexual orientation are subject to rational basis review” and the arguments it advanced were under that “binding standard.”

By contrast, he said, Windsor and Pederson require the department to “take an affirmative position on the level of scrutiny that should be applied to DOMA §3″ in the Second Circuit, which is “without binding precedent on the issue.”

Andrew Ehrlich of Paul Weiss said the parties in Windsor and Pedersen are now waiting to see if Congress will decide to fight the issue and send lawyers of its own to federal courthouses in New York and Connecticut.

“Presumably, House Republicans will retain some law firm to defend the statute,” Mr. Ehrlich said. “That is an extremely infrequent occurrence and I think it underscores how historic this decision is.”

The move quickly drew praise from some Democrats in Congress but a sharp response from the spokesman for Mr. Boehner, the Republican House Speaker.

“While Americans want Washington to focus on creating jobs and cutting spending, the president will have to explain why he thinks now is the appropriate time to stir up a controversial issue that sharply divides the nation,” said Mr. Boehner’s spokesman, Michael Steel.

The U.S. Supreme Court has not yet ruled on the level of scrutiny that applies to DOMA cases, but Mr. Holder argued in his letter to Mr. Boehner that Supreme Court cases defining when heightened scrutiny should be used make it clear that the standard should be applied to DOMA as well.

He cited the “significant history of purposeful discrimination against gay and lesbian people,” and a “growing scientific consensus” that “accepts that sexual orientation is immutable.”

The attorney general acknowledged that the adoption of restrictive laws and policies aimed at homosexuals, such as the absence of federal protection for employment discrimination on the basis of sexual orientation, show gays as a group have limited political power.

“And while the enactment of the Matthew Shepard Act and the pending repeal of [the military's] Don’t Ask Don’t Tell [policy] indicate the political process is not closed entirely to gay and lesbian people,” he said, “that is not the standard by which the Court has judged ‘political powerlessness.’”

Finally, Mr. Holder said that “there is a growing acknowledgment that sexual orientation” has nothing to do with a person’s ability to perform or contribute to society. He cited “evolutions” in legislation, community practices and attitudes, case law and in the social sciences, all of which make clear that “sexual orientation is not a characteristic that generally bears on legitimate policy objectives.”

Mr. Holder said it was normally the job of his department to defend statutes if reasonable arguments can be made in their defense, but the department has broken with that tradition in instances where it “does not consider every plausible argument to be a ‘reasonable’ one.”

“This is the rare case where the proper course is to forgo defense of the statute,” he said.

Mr. Holder said in a statement that the Obama administration would continue to enforce Section 3.

“But while both the wisdom and the legality of Section 3 of DOMA will be the subject of both extensive litigation and public debate, this Administration will no longer assert its constitutionality in court,” he said.