* Massachusetts challenging Defense of Marriage Act

* State says federal law is "discriminatory"

* State seeks federal benefits for married gay couples (Adds details, reaction)

By Jason Szep

BOSTON, July 8 (Reuters) - Massachusetts sued the U.S. government on Wednesday to seek federal marriage benefits for about 16,000 gay and lesbian couples who have wed since the state became the nation's first to legalize same-sex marriage.

The state is challenging the constitutionality of the federal 1996 Defense of Marriage Act, saying it denies "essential rights and protections" to married gay couples.

The federal government is interfering with the state's "sovereign authority to define and regulate marriage," said the lawsuit filed in federal court in Boston. It calls the law "overreaching and discriminatory."

Others have challenged the law in the past but Massachusetts is the first state to do so. "We view all married persons equally and identically," Massachusetts Attorney General Martha Coakley told a news conference.

The lawsuit is the latest skirmish over gay marriage in the U.S. federal court system after a handful of political filmmakers led by a Democratic consultant crafted a gay rights challenge in May that they hope will reach the Supreme Court.