WASHINGTON  Many people knowledgeable about the federal budget said House Republicans could not keep their campaign promise to cut $100 billion from domestic spending in a single year. Now it appears that Republicans agree.

As they prepare to take power on Wednesday, Republican leaders are scaling back that number by as much as half, aides say, because the current fiscal year, which began Oct. 1, will be nearly half over before spending cuts could become law.

While House Republicans were never expected to succeed in enacting cuts of that scale, given opposition in the Senate from the Democratic majority and some Republicans, and from President Obama, a House vote would put potentially vulnerable Republican lawmakers on record supporting deep reductions of up to 30 percent in education, research, law enforcement, transportation and more.

Now aides say that the $100 billion figure was hypothetical, and that the objective is to get annual spending for programs other than those for the military, veterans and domestic security back to the levels of 2008, before Democrats approved stimulus spending to end the recession.