WASHINGTON – An increasing number of attorneys general are refusing to defend state laws banning same-sex marriage, drawing fire from critics who believe it is their duty to protect these statutes against challenges under federal law.

Since two landmark decisions on same-sex marriage by the Supreme Court last year, gay marriage advocates have turned their attention to legal challenges to state laws prohibiting such unions.

After the Supreme Court left standing in June an order striking down California’s ban on gay marriage, without ruling whether similar laws should remain in place, federal appeals courts have been left dealing with the issue.

Gay couples are filing lawsuits in states where voters approved anti-gay marriage amendments to their state constitutions. Judges have recently struck down same-sex marriage bans in Kentucky, Ohio, Virginia, Oklahoma, Utah, and Texas.

The Supreme Court issued two major rulings on same-sex marriage last year. In United States v. Windsor, the court found unconstitutional a part of the Defense of Marriage Act (DOMA), which withheld federal recognition of same-sex marriages and denied federal benefits to those in such unions.

In the other case, the Supreme Court allowed to stand a federal judge’s opinion that California’s Proposition 8, which bans same-sex marriage, was unconstitutional.

In 2011, Attorney General Eric Holder refused to defend DOMA in court, but announced the Department of Justice would continue to enforce the law while it existed.

Same-sex marriage is legal in 17 U.S. states and the District of Columbia.

The nation’s highest court has not weighed in on whether same-sex couples have a constitutional right to marry, shifting the legal battleground, for now, to the states.

Six attorneys general – all Democrats – have decided against defending their states’ gay marriage bans from challenges. Attorneys general in Nevada, Oregon, Pennsylvania and Virginia have refused to defend bans on gay marriage. Similarly, attorneys general in California and Illinois refused to defend bans that were later overturned by the states.

Speaking in a panel discussion at the Heritage Foundation on Friday, former Virginia Attorney General Ken Cuccinelli said attorneys general can only decline to defend laws that are “blatantly unconstitutional.”

“The standard for attorneys general declining to defend state law or constitutional provision has been consistent for many years,” Cuccinelli said. “An attorney general must defend anything not blatantly unconstitutional, not ones that he or she really want to be unconstitutional, but that it is, as a matter of objective law, clearly against the Constitution.”

Last month, Holder said in a New York Times interview that state attorneys general do not have to defend laws they consider discriminatory, including bans on gay marriage. A few days later, Holder argued in a speech to the National Association of Attorneys General that laws distinguishing among people based on their sexual orientation violate the Constitution’s equal protection clause, citing the Supreme Court’s decision in United States v. Windsor.