Conservatives are gearing up for a showdown on the House floor over an across-the-board spending cut that would trim the federal government by an additional $20 billion this year. The amendment, which will be offered by a member of the Republican Study Committee, would reduce spending on top of the $100 billion in cuts already proposed by GOP leaders.

House Republicans, keeping their promise for an open amendment process, have devoted the entire week to a debate on the fiscal 2011 continuing resolution. With the current spending plan set to expire March 4, Republicans are using the bill to make cuts to discretionary spending.

Hundreds of amendments are expected to be filed, but the RSC’s across-the-board cut stands out as one of the largest.

The move comes after GOP leaders made notable progress last week toward the magic number of $100 billion in non-security discretionary spending cuts as outlined in the Pledge to America. The current proposal includes $81 billion in cuts, plus another $19 billion from security spending. The RSC hopes to achieve a full $100 billion in non-security spending.

It is anyone’s guess how the debate might play out on the House floor. GOP leaders have publicly said they will support additional cuts. But the RSC, despite its 175 members, might not have the votes to close the gap.

Still, conservatives have already forced House appropriators back to the drawing board once and remain optimistic about their chances now that the debate has reached the floor.

Rep. Jim Jordan (R-Ohio), chairman of the RSC, applauded conservatives — including freshman lawmakers — for setting the right tone early in the spending debate.

“The window of time to fix the country is closing rapidly,” Jordan said. “I cannot underscore this enough. If we don’t get after it now, we may lose the opportunity to truly fix things and make it so our kids can enjoy the greatest nation in history.”