By Ros Krasny

BOSTON (Reuters) - Massachusetts Attorney General Martha Coakley has asked the U.S. Supreme Court to uphold a recent appeals court decision striking down parts of the federal law that defines marriage solely as the union of a man and a woman.

The request sets up a potential first consideration of a gay marriage case by the Supreme Court.

"The Defense of Marriage Act is a discriminatory and unconstitutional law that harms thousands of families in Massachusetts and takes away our state's right to extend marriage equality to all couples," Coakley said in a statement.

"It is our firm conviction that in order to truly achieve marriage equality, all couples must enjoy the same rights and protections under both state and federal law."

Coakley's 37-page brief asked the nation's highest court to uphold the decision that found denying federal benefits to married same-sex couples was unconstitutional.

The brief said that the state "normally would oppose further review in order to ensure that the judgment takes effect as soon as possible" but added that "the Commonwealth recognizes that DOMA's unconstitutionality is a question of national significance."

"It is important that the Court address the matter in a case that presents the full complement of DOMA's constitutional infirmities," the brief said.

Coakley's move was a response to a brief filed June 29 by the Bipartisan Legal Advisory Group (BLAG), appointed by the Republican majority in the U.S. House of Representatives, which wants the court to reverse the lower court ruling.

That brief said the appeals court ruling "invalidated a duly enacted Act of Congress."

OBAMA ADMINISTRATION ABANDONED LAW

Lawyers for BLAG have defended DOMA after the Obama administration essentially abandoned the law in 2011. Continued...