John R. Bolton, under secretary of state for arms control and internal security, is scheduled to appear to defend the government's policy.
He is expected to face a host of hostile questions from congressmen upset with the administration's dealing of the nuclear scandal in Pakistan.
Both Republican and Democrat lawmakers have recently showed their dismay at the administration's decision to allow Pakistan to pardon a scientist who confessed to selling nuclear secrets and technology to Iran, Libya and North Korea.
All three were considered rogue states by the Bush administration when they received nuclear materials from the Pakistani scientist, A.Q. Khan. Since then, Libya has abandon its nuclear program and handed over its nuclear equipment to the United States.
Other witnesses at the committee hearing include Henry D. Sokolski, executive director of the Non-proliferation Policy Education Center; Joseph Cirincione, director for non-proliferation, Carnegie Endowment for International Peace. and Victor Gilinsky, former commissioner, U.S. Nuclear Regulatory Commission.