John Bacon

USA TODAY

A federal judge who is raising a child in a same-sex relationship appeared poised Monday to overturn Oregon's ban on same-sex marriage.

But a national group that wants marriage defined as a union of a man and a woman asked a federal appeals court Monday to halt the proceedings in Oregon and allow the group to intervene in the case.

Judge Michael McShane said last week he would rule Monday at noon local time — 3 p.m. ET — on a lawsuit brought by four gay and lesbian couples challenging the ban that was approved by voters a decade ago.

"I think everybody in the state assumes he's going to strike down the law," John Eastman, chairman of the National Organization for Marriage, told USA TODAY. "I'm not making that assumption. But however he rules... we want to be heard."

The state's Democratic attorney general, Ellen Rosenblum, has declined to defend the law, saying last year's U.S. Supreme Court ruling that tossed out key parts of the federal Defense of Marriage Act made the state ban indefensible.

Judges have tossed out similar bans in a half dozen states since the Supreme Court decision.

Last week, McShane rejected NOM's request to intervene in the Oregon case. McShane ruled that the group had no standing in the case, leaving no litigants to oppose the effort to drop the ban.

"This case is an ugly example of inappropriate cooperation between the (Oregon) attorney general and the gay marriage lobby, both of whom want to redefine marriage," said Brian Brown, NOM's president, in announcing the appeal. The group asked the 9th Circuit Court of Appeals in San Francisco to halt the proceedings before McShane can rule -- or stay the ruling if McShane tosses out the ban.

Eastman previously had questioned whether McShane should preside over the case, claiming McShane was in the same position as the couples who filed the suit. McShane said in court last month he had no plans to wed his partner. That satisfied Eastman.

Oregon United For Marriage, which gathered signatures to qualify a same-sex marriage initiative for the ballot, has said it will drop the measure if McShane rules in favor of gay marriage.

Seventeen states and the District of Columbia have legalized same-sex marriage. Judges in seven other states have struck down bans on gay marriage, though appeals are pending in some states. More challenges are pending.

In Oregon, Portland attorneys Lake Perriguey and Lea Ann Easton filed a lawsuit in October on behalf of two women in a relationship for more than 30 years. Two months later, the American Civil Liberties Union and lawyers from two firms went to court on behalf of a lesbian couple and a gay couple.

Oregon's ban, approved by 57% of voters, came months after Multnomah County briefly issued marriage licenses to same-sex couples. Multnomah includes Portland and is the state's largest county.

About 3,000 gay couples were allowed to marry before a judge halted the practice. The Oregon Supreme Court later invalidated the marriages.

Contributing: Associated Press