Spending on outsourced worker services makes up the largest dollar chunk of U.S. government contracting, according to a March 11 Congressional Budget Office analysis for the House Budget Committee, but the agency can't determine how many jobs it funds.

Spending for professional, administrative and management services from the private sector grew the most in real dollas between 2000 and 2012, says CBO in a letter to Maryland Rep. Chris Van Hollen, ranking committee Democrat, who had requested information on the "size and cost of the federal government's contracted workforce."