The C.I.A. has placed the American-born cleric Anwar al-Awlaki on a list for killing. The notion that the government can, in effect, execute one of its own citizens,an American, born in New Mexico, far from a combat zone, with no judicial process and based on secret intelligence, makes some legal authorities deeply uneasy.

Harold Koh, the State Department’s legal adviser, approves under the general principle of self-defense. By those rules, he said, such targeted killing was not assassination, which is banned by executive order.