WASHINGTON (AFP) – Top US House of Representatives leaders voted along party lines Wednesday to defend in court a law defining marriage as only between a man and a woman after President Barack Obama repudiated it.

The House Bipartisan Legal Advisory Group voted 3-2 to direct the chamber's general counsel to take action to enforce the Defense of Marriage Act (DOMA), which has been in effect for 15 years.

Obama's Republican foes, led by House Speaker John Boehner, voted in favor of the move, while the White House's Democratic allies, led by House Minority Leader Nancy Pelosi, voted against it.

"This action by the House will ensure that this law's constitutionality is decided by the courts, rather than by the president unilaterally," Boehner said in a statement.

US Attorney General Eric Holder said in a late February letter to Boehner that Obama had concluded the law was unconstitutional.

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Obama had found that by excluding same-sex couples from legal marriage, the law "violates the equal protection component of the Fifth Amendment," and that his administration would no longer defend it, Holder wrote at the time.

Pelosi said Obama's decision amounted to "a bold step forward for civil rights" and called the law "unfair and indefensible" and a betrayal of "our nation's long-held and long-cherished value of equality for all."

"The House should not be in the business of defending an unconstitutional statute that is neither rational nor serves any governmental interest," she said, bluntly questioning the cost and effectiveness of any resulting legal action.

"Given the complexity and number of cases, this legal challenge would sap hundreds of thousands of taxpayer dollars, if not more, during a time of limited fiscal resources."

A senior Democratic aide said that House General Counsel Kerry Kirchner warned the leaders that legal action would "not be inexpensive" and would take a minimum of 10 months.

Pelosi noted that there were ongoing cases dealing with the law and said that meant that House action was unnecessary, said the aide, who requested anonymity.

And Kirchner detailed how former US president Ronald Reagan had stopped defending five laws in the 1980s, the aide said, adding that "clearly Republicans were fine with a Republican president choosing not to defend" existing statutes.