House Republicans have quietly raised the value of a contract with a private law firm that is handling the chamber’s Supreme Court defense of a 1996 federal law that defines marriage as the union between a man and a woman.

House Administration Chairman Dan Lungren, R-Calif., signed off in September on a $500,000 increase in the maximum value of the contract with the firm, Washington-based Bancroft. Republicans have raised the cap of the contract twice: first on Sept. 29, 2011, from its original maximum of $500,000 to $1.5 million, and again on Sept. 28 to its new maximum of $2 million.

Although the latest lifting of the contract cap occurred almost three months ago, House Democrats — and the public — were in the dark about the move until this week. House Republicans did not share the revised contract with Democrats until Thursday, according to Drew Hammill, a spokesman for Minority Leader Nancy Pelosi, D-Calif. Hammill provided a copy of the contract modification to CQ Roll Call.

Indeed, Democrats were so out of the loop that Pelosi’s office released figures on Oct. 16 showing that the taxpayer expenses for the defense of the law nearly had hit their cap of $1.5 million. But that was almost three weeks after Lungren had raised the cap to $2 million.

Pelosi blasted House Republicans in a statement Thursday for “wasting taxpayer dollars to defend the indefensible Defense of Marriage Act.”

“Hiding this contract from voters in the midst of an election season was a cynical move at best, and a betrayal of the public trust at worst,” she said. “Republicans should not be spending $2 million to defend discrimination in our country.”

Republicans have been forced to raise the contract’s maximum value as legal challenges to the Defense of Marriage Act have mounted in courts across the country. The GOP-led House is defending the measure because the Obama administration decided in February 2011 that it views the statute as unconstitutional and will no longer do so.

The Supreme Court agreed Dec. 7 to evaluate the constitutionality of the statute, which prevents same-sex couples who are married legally under state law from receiving a host of federal benefits. The court is expected to hear arguments in March, with a decision likely by the end of June.

In an interview Thursday, Lungren said he did not know whether the Supreme Court’s review of DOMA — and the heavy workload it might put on Bancroft and its lead attorney, former solicitor general Paul D. Clement — would force Republicans to raise the contract cap again in the future.

Lungren noted that besides evaluating the constitutionality of the statute itself, the court has asked whether the House has the standing to defend the measure in court. That question, he said, could add to Bancroft’s workload because it might require additional briefing and preparation.

“I don’t know whether that would require more expenditure of funds, but it is a serious argument that has to be seriously dealt with,” said Lungren, who lost his re-election bid and will be succeeded as head of the committee next year by Rep. Candice S. Miller, R-Mich.

Other observers, however, have said that the taxpayer costs of the legal defense may taper off now that the high court has stepped in, since the justices’ review of the law has put similar cases in the lower courts on hold.

The question of taxpayer costs has been a delicate one for House Republicans, who have remained largely silent on DOMA even as Democrats have sharply criticized them for using public money to defend the statute. Speaker John A. Boehner, R-Ohio, was asked about the rising costs at a news conference Thursday, but gave a one-sentence reply.

“If the Justice Department is not going to enforce the law of the land, the Congress will,” Boehner said.

House Republicans initially said they would tap the Justice Department’s budget to mount their legal defense of the marriage law, since it was the department that stopped defending the statute.

In reality, however, much of the funding for the legal defense has come from the legislative branch budget — specifically, from the “salaries, officers and employees” account of the Chief Administrative Officer, according to congressional testimony.

The House tapped $742,000 from that account to pay for its defense of the marriage law, Chief Administrative Officer Dan Strodel testified before a House Appropriations subcommittee in March.

Since that time, the costs for the legal defense have increased sharply. But it is unclear whether the additional money also has been transferred from the Chief Administrative Officer’s budget or from other sources. A spokesman for the Chief Administrative Officer could not immediately confirm that the additional funding came from the agency’s budget.