President Barack Obama has decided that a federal law against gay marriage is unconstitutional and will no longer defend it in court, the Justice Department announced Wednesday.

However, Obama will continue to enforce the law, called the Defense of Marriage Act, until it is either struck down by the courts or repealed by Congress, which he has urged, according to White House press secretary Jay Carney.

The law, passed by a Republican Congress and signed into law by Democratic President Bill Clinton in 1996, defined marriage as between one man and one woman.

“”Much of the legal landscape has changed in the 15 years since Congress passed DOMA,”” Attorney General Eric Holder said in a statement.

“”The Supreme Court has ruled that laws criminalizing homosexual conduct are unconstitutional. Congress has repealed the military’s ‘don’t ask, don’t tell’ policy. Several lower courts have ruled DOMA itself to be unconstitutional.””

He said that the Justice Department had a long-standing practice of defending the constitutionality of laws as long as “”reasonable arguments”” could be made for them. But he said the department also has refused to defend laws when the president has concluded they are unconstitutional.

In July, a federal district judge in Massachusetts ruled the law unconstitutional, saying it violates gay couples’ right to equal protection and states’ rights to set their own marriage laws.The Obama Justice Department had defended the law, even while calling it “”discriminatory”” and supporting its repeal.