Rosenblum's decision provides a significant boost for two federal lawsuits challenging the state's voter-approved ban, although she said Oregon would continue to prohibit same-sex marriage until the courts or voters say otherwise.
In particular, Rosenblum's decision led backers of a gay marriage ballot measure campaign to contemplate the prospect of being able to drop their initiative.
Officials of Oregon United for Marriage said they would not submit signatures to qualify their initiative for the November ballot until seeing how U.S. District Judge Michael McShane rules.
"If we get marriage (from the federal court) in the spring and nobody appeals and marriage licenses are being issued, nobody has any hunger for a ballot measure we don't need," said Mike Marshall, campaign manager for Oregon United.
With both the plaintiffs -- four gay and lesbian couples seeking the right to marry -- and the state agreeing that the ban is unconstitutional, it is possible there would be no one with the legal standing to appeal if McShane strikes down the state's ban.
That left opponents fuming and saying that Rosenblum was failing to do her job.
The Oregon Family Council, which has been active in opposing the initiative, charged that Rosenblum "has ignored her duty to defend the Oregon Constitution and the will of the majority of Oregonians that approved Measure 36 in 2004."
Jack Louman, executive director of the council, said in a statement that the governor or attorney general needs to appoint someone with the legal standing "before the court to represent natural marriage on behalf of the state."
Louman added that it was "an outright attack on democracy" for an amendment approved by voters "to have no defense in federal court."
In a press conference, Rosenblum insisted that her decision had nothing to do with her personal opinion on gay marriage and "everything to do with the constitution of the United States" and a string of decisions by federal judges striking down state laws prohibiting same-sex marriage.
Asked how she would describe this decision not to defend a voter-approved constitutional amendment, Rosenblum said: "We say that the United States Constitution has been violated in our opinion by this state constitutional provision."
Rosenblum, a Democrat, joins at least five other attorneys general -- in California, Pennsylvania, Illinois, Nevada and Virginia -- who have refused to defend prohibitions against gay marriage.
