"Discretionary spending is provided and controlled through appropriations acts, which fund many of the activities commonly associated with such federal government functions as running executive branch agencies, congressional offices and agencies, and international operations of the government. Essentially all spending on federal wages and salaries is discretionary. Federal spending in 2009 accounted for just under a quarter (24.7%) of the U.S. economy, as measured by gross domestic product (GDP). Federal spending since 1962 has averaged about a fifth of GDP. (Years denote federal fiscal years unless noted otherwise.) Discretionary spending accounted for 35.2% of total outlays in 2009, as extraordinary federal responses to financial turmoil sharply increased mandatory spending (59.5% of outlays in 2009), reducing discretionary spending's share of total spending. [...] The Obama Administration in its recent budget submission called for a three-year freeze on nonsecurity discretionary spending. Weak economic conditions have depressed federal revenues and may continue to increase government social safety-net expenditures. Some contend that additional stimulus measures are needed to reduce high unemployment levels, while others have called for imposing greater budgetary stringency. Over the long term, projected future growth in entitlement program outlays may put severe pressure on discretionary spending unless policy changes are enacted or federal revenues are increased. This report will be updated as events warrant." This CRS (Congressional Research Service) report also addresses Homeland Security and Defense spending.
CRS Report for Congress, RL34424