WASHINGTON - The Obama administration said Wednesday it will stop enforcing a law that blocks benefits to partners of military veterans in same-sex marriages.

In a letter to congressional leaders, Attorney General Eric Holder said that a provision in federal law on benefits to veterans and their families defines "spouse" to mean a person of the opposite sex. He says that definition leaves out legally married same-sex couples, and runs afoul of a June Supreme Court ruling.

The court declared unconstitutional a provision in the Defense of Marriage Act restricting the words marriage and spouse to apply only to heterosexual unions. Holder says that like the Defense of Marriage Act, the provision in the veterans benefits law has the effect of placing lawfully married same-sex couples in a second-tier marriage.

"Decisions by the Executive not to enforce federal laws are appropriately rare," Holder told Congress. "Nevertheless, the unique circumstances presented here warrant non-enforcement."

He said the Supreme Court's conclusion that DOMA imposes a stigma on everyone in same-sex marriages "would seem to apply equally" to the veterans benefits law. Holder noted that after the Supreme Court's decision, the Bipartisan Legal Advisory Group of the House of Representatives withdrew from a pending lawsuit challenging the constitutionality of the veterans benefits provisions.

President Barack Obama directed the executive branch to cease enforcement of the provision, Holder wrote.

Last week, a federal judge in Los Angeles ruled that a lesbian Army veteran and her spouse should be entitled to disability benefits, given the Supreme Court's recent ruling.

U.S. District Judge Consuelo Marshall said that federal law defining a spouse as a person of the opposite sex is unconstitutional since the high court's decision allowing legally married gay couples the right to health care benefits.

Although the Supreme Court did not directly address the constitutionality of the veterans benefits provisions, the reasoning of the opinion "strongly supports the conclusion that those provisions are unconstitutional," Holder wrote.

The Justice Department has been tapped by the White House to ensure that couples in same-sex marriages receive all federal benefits to which they are entitled. The Social Security Administration says it has started processing spousal retirement claims for same-sex couples and paying benefits. Last week, the government said that all legally married gay couples will be able to file joint federal tax returns even if they reside in states that do not recognize same-sex marriages.

Many of the changes are relatively easy to make because they involve federal regulations, but the veterans benefits present a more difficult issue because that prohibition is part of federal law.

"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," Holder wrote.

Because of the way federal law on the Department of Veterans Affairs is worded, Wednesday's announcement does not apply to same-sex couples who live in a state that does not recognize gay marriage. Justice Department spokesman Brian Fallon said the issue is under review.

A gay rights group says it's a problem. "We would like to see the Department of Veterans Affairs adopt a standard where the agency accepts a valid marriage license from any jurisdiction," said Michael Cole-Schwartz, a spokesman for Human Rights Campaign, the nation's largest lesbian, gay, bisexual and transgender political organization.

"There's no reason to treat veterans who live in one state differently than veterans who happen to live in a state that doesn't recognize them," Cole-Schwartz said.