Last week, a Federal District Court judge ruled that the veterans spouse statute was unconstitutional, but that ruling applied only to the specific plaintiffs and the legal issue has not been reviewed by an appellate court. But in his letter on Wednesday, Mr. Holder said there was no point in waiting for a more definitive result.

“In the meantime, continued enforcement would likely have a tangible adverse effect on the families of veterans and, in some circumstances, active-duty service members and reservists, with respect to survival, health care, home loan and other benefits,” he wrote.

The decision does not mean that every same-sex couple is eligible for spousal benefits. Another part of the statute defines spouses as those whose marriages are recognized by the state where they live or where the veteran was discharged — not the state where the marriage occurred. The Supreme Court’s ruling said that the federal government could not discriminate against same-sex couples whose marriages were recognized under state law, but it did not create a right to have one’s marriage recognized in federal law when the state does not sanction it.

The Obama administration’s decision to stop obeying the law without a definitive court ruling is a new step in its increasingly aggressive approach to providing same-sex marriage rights.

Early in his presidency, when Democrats controlled both chambers of Congress, Mr. Obama said that laws discriminating against same-sex couples should be scrapped. But he urged lawmakers to amend them, even as his Justice Department defended Congress’s constitutional right to enact such laws in court.

In December 2010, the administration pushed Congress to eliminate the law barring gay and lesbian troops from serving openly in the military. But in early 2011, after Republicans took control of the House of Representatives, Mr. Holder informed Congress that the Justice Department had decided that the Defense of Marriage Act was unconstitutional and that it would no longer defend the law in court.

Soon after, Mr. Holder sent another letter to Congress saying the administration had come to the same conclusion on the veterans law. But he also said in both letters that the administration would continue to enforce the disputed laws until a court definitively ruled them to be unconstitutional.