A federal judge has found a federal law that bans gay marriage to be unconstitutional.

The ruling handed down Thursday by US District Court Judge Joseph L Tauro says the Defense of Marriage Act (DOMA) violates the Fourteenth Amendment's equal protection guarantee.

The case, Gill v. Office of Personnel Management, is being litigated by the Boston-based gay rights group Gay & Lesbian Advocates & Defenders (GLAD), the group at the center of the gay marriage debate in New England.

GLAD is representing seven married gay couples and three surviving spouses from Massachusetts who have been denied federal benefits because of the 1996 law that defines marriage as a heterosexual union for federal agencies. President Bill Clinton signed DOMA into law.

Mary L. Bonauto argued that the law is an unconstitutional intrusion on a matter previously left to the states. Lawyers representing the government asked for the suit to be dismissed.

“This presidential administration disagrees with DOMA as a matter of policy,” W. Scott Simpson, a DOJ lawyer argued. “But that does not affect its constitutionality.”

Tauro ruled in the group's favor without a trial.

The ruling is certain to be appealed and is among the three gay marriage cases expected to eventually reach the Supreme Court.

The state of Massachusetts has filed a similar challenge in federal court to DOMA. And a ruling is expected shortly in a case that questions the constitutionality of California's gay marriage ban, Proposition 8.

GLAD's case focuses narrowly on federal benefits being denied to legally married couples in Massachusetts, the first state to legalize the institution in 2004.