BOSTON (Reuters) - In a victory for gay rights in the United States, a U.S. district court judge in Massachusetts ruled on Thursday that a federal ban on same-sex marriage is unconstitutional.

Supporters of gay marriage rally outside the federal courthouse in San Francisco, California January 11, 2010. REUTERS/Robert Galbraith

Judge Joseph Tauro in Boston ruled in favor of gay couples’ rights in two separate challenges to the 1996 Defense of Marriage Act, known as DOMA, arguing that the law interferes with the right of states to define marriage.

Massachusetts had argued DOMA denied benefits to same-sex couples in the state, where such unions have been legal since 2004. Four other states -- Vermont, New Hampshire, Connecticut and Iowa -- also allow same-sex marriage, as does Washington, D.C.

Tauro agreed with the state’s argument and said DOMA forces Massachusetts to discriminate against its own citizens.

“The federal government, by enacting and enforcing DOMA, plainly encroaches upon the firmly entrenched province of the state, and in doing so, offends the Tenth Amendment,” Tauro said. “For that reason, the statute is invalid.”

The Tenth Amendment of the U.S. Constitution says: “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

The Justice Department argued the federal government can determine eligibility requirements for federal benefits, including requiring that those benefits go only to couples in marriages between a man and a woman.

CONSERVATIVES CONFIDENT

The federal government has 60 days to decide whether to appeal Tauro’s rulings to the U.S. Court of Appeals for the First Circuit, also in Boston.

Conservative groups predicted the ruling would be overturned.

“This activist decision must be appealed, and when appealed, I am confident it will be reversed,” said Mathew Staver, founder of the legal group Liberty Counsel, based in Orlando, Florida.

“History and common sense show that marriage between a man and a woman has a procreative component absent from same-sex unions,” Staver said.

In a second case, filed by civil rights group Gays & Lesbian Advocates & Defenders (GLAD), Tauro ruled that DOMA violates the Constitution’s equal protection clause.

Under the ruling, the plaintiffs -- seven married same-sex couples and three widowers from Massachusetts -- would be entitled to the same federal spousal benefits and protections as opposite-sex married couples.

Nancy Gill, one of the plaintiffs in GLAD’s suit, is a 22-year employee of the U.S. Postal Service who cannot cover her wife, Marcelle Letourneau, on her family health and vision insurance plans.

“I am thrilled that my family will now be treated in the same way as those of my married co-workers at the post office,” Gill said.

Chad Griffin, spokesman for the American Foundation for Equal Rights, applauded the rulings.

“Our courts exist to protect Americans’ constitutional rights when they are violated, and this decision affirms the equal rights of gays and lesbians,” Griffin said.

Congress enacted DOMA when it seemed that Hawaii was on the verge of legalizing gay marriage, and opponents feared that the movement would become a nationwide trend. States allowing same sex marriage are still a small minority.