BOSTON -- Massachusetts Democrats are faulting Republican U.S. Senate hopeful Michael Sullivan on the issue of gay marriage even as Sullivan scrambled to say he opposes a federal law that bars benefits for same-sex couples.

Democratic Party Chairman John Walsh said Sullivan is out of touch with Massachusetts, which became the first state to legalize gay marriage in 2004. "One issue people in Massachusetts have decided is equal marriage rights for our gay and lesbian neighbors," Walsh said.

Sullivan said Wednesday he's a "traditionalist" on marriage, believing it should be between a man and a woman.

"I don't know how controversial that is. (President Barack) Obama himself has essentially described himself as a traditionalist when it came to the definition of marriage. John Kerry, I understand, has essentially taken the same position," Sullivan said after dropping off voter signatures guaranteeing himself a spot on the GOP primary ballot.

Obama and Kerry have since voiced support for gay marriage.

Later Wednesday, Sullivan's campaign issued a statement saying he believes the federal Defense of Marriage Act should be overturned. The act denies legally married gay couples a range of federal benefits available to married same-sex couples.

"I recognize that gay marriage is legal in Massachusetts," he said. "I've done nothing to undermine that. I respect the fact that there are loving relationships among same-sex people."

A challenge to the Defense of Marriage Act's definition of marriage as between a man and a woman is expected to be heard later this month by the U.S. Supreme Court.

Sullivan is the only candidate in the race who has said he is opposed to gay marriage.