Incoming Democratic committee chairmen say they will hold a series of hearings and investigations early next year to build the case for their call for a phased withdrawal of U.S. troops from Iraq and for possible action against defense contractors found to have wasted billions in federal funds.

The emerging plans to grill administration officials on the conduct of the war are part of a pledge for more aggressive congressional oversight on issues such as prewar intelligence, prisoner treatment at Abu Ghraib and Guantanamo Bay, and the government’s use of warrantless wiretaps.