A group of 40 House Republicans for the first time Wednesday encouraged Congress’s deficit reduction committee to explore new revenue as part of a broad deal that would make a major dent in the nation’s debt, joining 60 Democrats in a rare bipartisan effort to urge the “supercommittee” to reach a big deal that could also include entitlement cuts.

The letter they sent represents a rare cross-party effort for the rancorous House, and its organizers said they hoped it would help nudge the 12-member panel to reach a deal that would far exceed the committee’s $1.5 trillion mandate.

Among those who signed were several dozen Republicans who had previously signed a pledge promising they would not support a net tax increase. Among the Democratic signers were some of the House’s most liberal members who have opposed entitlement cuts.

Rep. Emanuel Cleaver II (D-Mo.), chairman of the Congressional Black Caucus, said the effort was to help Congress avoid being “cornered by the paralysis of small potatoes.” Rep. Cynthia M. Lummis (R-Wyo.), a member of the conservative Republican Study Group, said the intent was to compel the supercommittee to craft a strategy “so big, so comprehensive, so inclusive that any great statesman or stateswoman could hardly resist voting for it.”

“To succeed, all options for mandatory and discretionary spending and revenues must be on the table,” the group wrote, adding that previous deficit reduction task forces have suggested a goal of reducing the debt by $4 trillion over the next decade. “Our country needs our honest, bipartisan judgment and our political courage.”

The letter comes as pessimism that the supercommittee can find agreement by a Nov. 23 deadline is running high on Capitol Hill.

Aides to both sides have said the six House members and six Senators who serve on the panel are stuck on the same issue that has divided previous efforts to cut the deficit — Democrats want Republicans to accept sizable new revenue generation before agreeing to significant entitlement cuts and Republicans do not want to back a tax increase.

Republican supercommittee members spent Wednesday shuttling between leadership offices, in discussions over potential revisions to an offer they sent to Democrats last week, aides said.

That proposal, which would slice $2.2 trillion from future borrowing over the next decade, included less than $100 billion in actual tax increases. Those increases would come entirely through revising the index used to measure inflation. Republicans argue they would get another $200 billion through encouraging economic growth.

Part of Wednesday’s discussion appeared to be whether to boost the tax offer by proposing to end some corporate subsidies such as tax breaks for oil and gas companies.

The bipartisan letter sent Wednesday included no specifics — it did not, for instance, commit its signers to supporting a tax increase, as many Democrats have urged, but merely urged that the committee consider revenue.

Still, Republicans said the number of members of their party who signed was significant, given fear among many members it would nevertheless be interpreted as endorsing taxes, particularly by Grover Norquist, the Americans for Tax Reform president. Norquist urges elected officials to sign a pledge that they will not raise taxes.

Rep. Steven C. LaTourette (R-Ohio) said if he had a nickel for every one of the Republicans who said they supported the letter’s goal but feared how Norquist would react, “I’d be rich and retired, and we’d have 200 signatures on the letter.”

LaTourette, a close ally of House Speaker John A. Boehner (R-Ohio), said the new coalition was a sign that Republican leaders are now willing to unite with Democrats on a grand bargain that would address both revenue and entitlements, even if it meant leaving behind some of the GOP’s hardline voices.

Norquist played down the letter’s significance, noting it merely asked the committee to consider all options.

“Consider anything,” he said. “Just don’t vote for a tax increase.”

And several Republicans who signed the letter were careful to note they were not endorsing a net tax increase — but rather a broad rewrite of the tax code that might close loopholes and lower rates, while still producing more government revenue.

The complex math of tax reform was highlighted Wednesday in a report from congressional tax analysts that cast doubt on a Republican plan to slash the corporate tax rate to 25 percent. The nonpartisan Joint Committee on Taxation concluded that eliminating existing loopholes and tax breaks would generate only enough cash to cut the rate to 28 percent.

The report was requested by Rep. Sander M. Levin (Mich.), the senior Democrat on the House Ways and Means Committee.

Levin noted in an interview that even getting the corporate rate down to 28 percent would require wiping out many critical tax incentives for manufacturers and the energy sector, a move many lawmakers may not want to take.

“If there’s a discussion of tax reform, it needs to be informed,” Levin said, “not just a stab in the dark.”

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