Mr. Obama and his advisers are still debating whether remote-control killing should be a measure of last resort against imminent threats to the United States, or a more flexible tool, available to help allied governments attack their enemies or to prevent militants from controlling territory.

Though publicly the administration presents a united front on the use of drones, behind the scenes there is longstanding tension. The Defense Department and the C.I.A. continue to press for greater latitude to carry out strikes; Justice Department and State Department officials, and the president’s counterterrorism adviser, John O. Brennan, have argued for restraint, officials involved in the discussions say.

More broadly, the administration’s legal reasoning has not persuaded many other countries that the strikes are acceptable under international law. For years before the Sept. 11, 2001, attacks, the United States routinely condemned targeted killings of suspected terrorists by Israel, and most countries still object to such measures.