In an abrupt development, the D.C. City Council on Tuesday voted unanimously to back legislation allowing the city to recognize same-sex marriages performed in other states and countries as legal marriages in the District of Columbia.

The Council approved the marriage recognition measure, 12-0, in a “first reading” vote as an amendment to an unrelated bill dealing with city matters pending before federal courts. The bill must be approved in a second-reading vote slated for May 5.

D.C. Mayor Adrian Fenty, a longtime supporter of same-sex marriage rights, is expected to sign the bill if it clears the second vote. But before becoming law, the bill also must clear a required review by Congress for a period of 30 legislative days, which sometimes takes as long as 60 calendar days.

Most Capitol Hill observers expect at least some members of Congress to object to the legislation, with the possibility that one or more lawmakers could call on Congress to invoke its authority to overturn the marriage-recognition measure.

“A marriage legally entered into in another jurisdiction between two persons of the same sex that is recognized as valid in that jurisdiction, that is not expressly prohibited by [the city’s existing marriage law] shall be recognized as a marriage in the District,” the amendment says.

“I look at this as simply making explicit what is already in the law,” said D.C. Council member Phil Mendelson (D-At Large), who introduced the amendment.

Mendelson and Council member David Catantia (I-At Large), who is gay, said the city’s existing marriage law has recognized legally approved marriages from other jurisdictions since at least 1901. They said the Council’s decision to specifically allow recognition of same-sex marriages from other jurisdictions was merely a clarification of a longstanding tradition of recognizing marriages from other states and countries.

The Council’s move came less than a week after the Iowa Supreme Court handed down a decision legalizing same-sex marriage in that state. And it came on the same day that the Vermont Legislature overrode a veto by Republican Gov. Jim Douglas of a same-sex marriage rights bill, enacting the bill into law and making Vermont the nation’s fourth state to legalize gay marriage.

Iowa, Vermont, Connecticut and Massachusetts, which also have legalized same-sex marriage, don’t have residency laws that would prevent same-sex couples from D.C. to travel to those states to marry.

Catania had planned to introduce separate legislation in January to fully legalize same-sex marriage in the District. He postponed the introduction after activists said they were not ready to fend off expected opposition in Congress. The activists also said they needed more time to raise money and build a grassroots organization needed to fight an expected voter referendum to overturn any Council-approved gay marriage bill.

Some activists viewed Tuesday’s action by the Council on the marriage-recognition measure as a trial run for a full same-sex marriage rights bill.

“The collective assessment was that recognizing marriages from other jurisdictions, while not without risk on Capitol Hill, was the next logical step toward our goal of civil marriage equality in the District,” said Rick Rosendall, vice president of the Gay & Lesbian Activists Alliance.

“Let’s see whether and how Congress reacts to the marriage-recognition amendment, either during the bill’s congressional review period or during consideration of the D.C. appropriations bill this summer,” Rosendall said.

He was referring to a tactic sometimes employed by Congress to change or kill D.C. bills by adding hostile amendments to the city’s appropriations bill, which Congress must approve each year.

The Council also approved the marriage recognition amendment on the same day that it approved the Domestic Partnership Judicial Determination of Parentage Act of 2009, a separate bill that provides full parental rights for same-sex couples who raise children.

Mendelson said he decided to introduce the marriage recognition measure as an amendment to the unrelated federal courts bill, rather than to the domestic partner parentage bill, to make sure the partner bill is not delayed in the event that Congress raises objections to the marriage measure.

“There’s always the possibility that Congress could step in,” Mendelson said. “So I chose to put this in another bill.”

The marriage-recognition bill changes yet another domestic partnership bill that the Council approved last year and which became law after clearing the congressional review process. That measure, the Omnibus Domestic Partnership Equality Amendment Act of 2008, allowed the city to recognize same-sex marriages, civil unions or domestic partnerships performed by other states or countries as domestic partnerships in D.C.

The marriage-recognition amendment approved by the Council on Tuesday would remove the reference to marriage from the omnibus partner bill and allow for full city recognition of same-sex marriages from other states and countries. But it would leave in place the provision in the omnibus statute that allows the city to recognize same-sex civil unions and domestic partnerships from other states and countries as domestic partnerships in D.C.

All of the Council’s 13 members co-introduced the marriage recognition amendment, including Council member and former D.C. mayor Marion Barry (D-Ward 8), who was absent during Tuesday’s vote.

The Council’s vote approving the marriage-recognition measure in a unanimous first-reading vote came as a surprise to most city government observers because it had not been introduced as a regular bill and did not go through the normal committee hearing process.

Catania said he asked Mendelson to take up the amendment and that Mendelson agreed after the two held discussions over the matter with their Council colleagues and with LGBT activists who worked with the Council on previous domestic partnership bills.

“What we did today is not a substitute for marriage equality,” Catania told the Blade. “This is the next step, not the final step.”

Catania said he still plans to introduce a full same-sex marriage rights bill into the Council “in due course.” Asked if he would introduce such a bill this year, Catania said, “Yes.”

Gay Council member Jim Graham (D-Ward 1), who along with Catania has called for passing a full same-sex marriage bill, said the marriage recognition bill approved by the Council on Tuesday was an important first step for full marriage equality for gays and lesbians.

For more than four years, Graham has called on the city government to recognize same-sex marriages from other jurisdictions, saying he believed the existing marriage law allowed for such recognition.

“Residents of the District of Columbia have married in Massachusetts,” Graham told the Blade last year. “They have a right to know whether those marriages are going to be recognized when they return home.”