Yet conservative analysts say even more spending cuts are desirable. Brian Riedl of the Heritage Foundation, a conservative research organization, has outlined a plan for $343 billion in reductions, including cuts from corporate tax breaks and entitlement programs that are not in the portion of the federal budget that House Republicans are focusing on, the so-called nonsecurity discretionary spending.

“The difficulty for Republicans is that they’re concentrating their cuts in a small sliver of the budget,” Mr. Riedl said. “They should also be addressing large entitlement programs, such as Medicare and Social Security, which are the main source of our budget problems. Cutting $100 billion from these other programs isn’t just a matter of eliminating waste, fraud and abuse. It will involve real cuts in real programs.”

Other Republicans are skeptical, as well.

“I just don’t know how, when you get down to it, they’re going to get agreement on that,” said G. William Hoagland, who for many years was the Republican staff director of the Senate Budget Committee.

The promise to cut $100 billion this fiscal year  in effect, taking government operations to 2008 levels  would mean cuts of more than 20 percent across the board from the $477 billion that Congress allocated for such programs in the 2010 fiscal year, which ended Sept. 30.

Such across-the-board cuts “would have very damaging implications for the long-term growth of the economy and the long-term future of our work force,” said Jacob J. Lew, Mr. Obama’s budget director. He is preparing the administration’s budget for the 2012 fiscal year, which would continue a three-year freeze of the same domestic spending at 2010 levels.

“If you look in areas like education, if it was applied across the board it would mean eight million students would have their Pell grants reduced by an average of $700,” Mr. Lew said. “You obviously could make policy not to do that, but then you’d have to save a lot of money somewhere else.”