The Obama administration's decision to authorize the killing by the Central Intelligence Agency of a terrorism suspect who is an American citizen has set off a debate over the legal and political limits of drone missile strikes, a mainstay of the campaign against terrorism. The notion that the government can, in effect, execute one of its own citizens far from a combat zone, with no judicial process and based on secret intelligence, makes some legal authorities deeply uneasy. To eavesdrop on the terrorism suspect who was added to the target list, the American-born radical cleric Anwar al-Awlaki, who is hiding in Yemen, intelligence agencies would have to get a court warrant. But designating him for death, as C.I.A. officials did early this year with the National Security Council's approval, required no judicial review. Congress has protected Awlaki's cellphone calls," said Vicki Divoll, a former C.I.A. lawyer who now teaches at the United States Naval Academy. "But it has not provided any protections for his life. That makes no sense." But like the debate over torture during the Bush administration, public discussion of what officials call targeted killing has been limited by the secrecy of the C.I.A. drone program.