The Boston-based U.S. Court of Appeals for the 1st Circuit concluded that the Defense of Marriage Act, which defines marriage as between a man and a woman, discriminates against gay couples.

“Under current Supreme Court authority, Congress’ denial of federal benefits to same-sex couples lawfully married in Massachusetts has not been adequately supported by any permissible federal interest,” Judge Michael Boudin wrote for the three-judge panel.

Plaintiffs, including seven married same-sex couples and three widowers, said the law, which prevents them from filing joint federal tax returns or collecting survivor benefits from the Social Security retirement program, denied them equal protections guaranteed under the U.S. Constitution.

In a companion case also on appeal, Massachusetts Attorney General Martha Coakley argued that Congress overstepped its authority and violated the Tenth Amendment of the U.S. Constitution in passing DOMA, because the law undermined states’ abilities to recognize marriage equality.

Lawyers for the Bipartisan Legal Advisory Group of the U.S. House of Representatives (BLAG) had defended the 1996 law, which the Obama administration essentially abandoned in 2011.

A federal judge in Massachusetts declared a key section of DOMA unconstitutional in 2010, and the appeals court agreed. Massachusetts legalized same-sex marriage in 2004, the first U.S. state to do so.

The appeals court recognized that many Americans believe marriage to be a union between a man and a woman. But the panel concluded that federalism permits diversity of governance based on local decisions, and that choice also applied to states’ decisions to legalize same-sex marriage.

Paul Clement, a lawyer for BLAG, was not immediately available for comment.

Coakley welcomed the decision. “It is unconstitutional for the federal government to create a system of first- and second-class marriages,” she said in a statement.

“The court couldn’t be clearer that these plaintiffs have the right to secure equal treatment under the law,” said Mary Bonauto, a lawyer with the Massachusetts advocacy group Gay and Lesbian Advocates and Defenders who served as lead attorney for the 17 plaintiffs.

Among the plaintiffs is Dean Hara, the widower of former U.S. Congressman Gerry Studds, who died in 2006. Studds, the first openly gay member of Congress, and Hara were married one week after same-sex marriages became legal in Massachusetts. Hara is not eligible to receive the pension provided to surviving spouses of former members of Congress.

Kris Mineau, president of the Massachusetts Family Institute, criticized the ruling as a blatant attack on the traditional definition of marriage.

“For a Massachusetts-based court to just audaciously proclaim that the federal government is wrong and has to recognize a unique social experiment in Massachusetts for the purpose of providing benefits is bizarre and a violation of the principles of our federalist system,” he said.

On May 24, a California federal judge found DOMA unconstitutional for denying federal benefits to same-sex couples. Another federal judge in San Francisco reached the same conclusion in February in a case currently on appeal before the 9th U.S. Circuit Court of Appeals. DM

Photo: Two men kiss as they sit in a riverside park in New York, May 9, 2012. After years of “evolving” on the issue, President Barack Obama said on Wednesday he believes same-sex couples should be allowed to marry, a stance that is likely to please his political base and complicate efforts to attract some independent voters. REUTERS/Lucas Jackson