The Obama administration announced Wednesday that it will no longer defend the federal law that defines marriage as a union between a man and a woman.

The decision marks a significant about-face for the Obama Justice Department, which until now had defended the law in court despite President Obama's misgivings with the policy. The administration's attorneys as recently as last month had filed a court motion in support of the Defense of Marriage Act, which effectively bans recognition of same-sex marriage.

But after two new lawsuits were filed in New York and Connecticut, Obama ordered Attorney General Eric Holder not to defend the statute.

"I fully concur with the president's determination," Holder said in a statement, declaring the provision to be "unconstitutional."

Holder said members of Congress may step up to defend the statute, but the Justice Department "will cease defense."

He noted that the congressional debate during passage of the Defense of Marriage Act "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 (Constitution's) Equal Protection Clause is designed to guard against."

Holder wrote to House Speaker John Boehner that Obama concluded the law fails to meet a rigorous standard under which courts view with suspicion any laws targeting minority groups who have suffered a history of discrimination.

Boehner's office was taken aback by the move, suggesting it was a bit off-topic considering the high-profile battle lawmakers are waging on Capitol Hill over federal spending.

"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," Boehner spokesman Michael Steel told Fox News.

Sen. Barbara Feinstein, D-Calif. said as a member of the Senate Judiciary Committee, she intends to introduce a bill that would repeal the act once and for all.

"My own belief is that when two people love each other and enter the contract of marriage, the federal government should honor that," she said in a statement. "I opposed the Defense of Marriage Act in 1996. It was the wrong law then; it is the wrong law now, and it should be repealed."

Maggie Gallagher, chairwoman of the National Organization for Marriage, said that if somebody from the House steps in to defend the law, it could actually be "good news" for Defense of Marriage Act supporters.

"This fight is not over yet. It's really just begun," she told Fox News.

Gay-rights groups applauded the administration. The Human Rights Campaign called the decision a "monumental" move against a law that "unfairly discriminates against Americans."

"Congressional leaders must not waste another taxpayer dollar defending this patently unconstitutional law," Human Rights Campaign President Joe Solmonese said in a statement.

"The Obama administration's decision is a victory for civil rights, fairness, and equality for the LGBT community and all Americans," House Democratic Leader Nancy Pelosi said.

The administration previously has defended laws with which the president disagrees, notably the "don't ask, don't tell" provision banning gays from serving openly in the military -- though that law was later repealed. Holder acknowledged this in his statement, but said there are exceptions.

"The department has a longstanding practice of defending the constitutionality of duly-enacted statutes if reasonable arguments can be made in their defense. At the same time, the department in the past has declined to defend statutes despite the availability of professionally responsible arguments, in part because -- as here -- the department does not consider every such argument to be a 'reasonable' one," Holder said. "Moreover, the department has declined to defend a statute in cases, like this one, where the president has concluded that the statute is unconstitutional."

Holder said the "legal landscape" has changed in the 15 years since the law was passed, citing the repeal of "don't ask, don't tell" and lower-court rulings against the law.

White House Press Secretary Jay Carney explained that the U.S. government will remain a party to Defense of Marriage Act cases so they can proceed in court. Though the administration says the key provision in the law is not constitutional, Carney said the administration will help others who want to defend it.

Obama, who supports the repeal of the Defense of Marriage Act, has said his views are "evolving" on same-sex marriage. Currently, he is only on record in support of civil unions.

The Associated Press contributed to this report.