The Obama administration has taken the extraordinary step of authorizing the targeted killingof an American citizen, the radical Muslim cleric Anwar al-Awlaki, who is believed to have shifted from encouraging attacks on the United States to directly participating in them, intelligence and counterterrorism officials said Tuesday. Al-Awlaki, who was born in New Mexico and spent years in the United States as an imam, is in hiding in Yemen. He has been the focus of intense scrutiny since he was linked to Maj. Nidal Malik Hasan, the Army psychiatrist accused of killing 13 people at Fort Hood, Texas, in November, and then to Umar Farouk Abdulmutallab, the Nigerian man charged with trying to blow up a Detroit-bound airliner on Dec. 25. American counterterrorism officials say al-Awlaki is an operative of al-Qaida in the Arabian Peninsula, the affiliate of the terror network in Yemen and Saudi Arabia. They say they believe that he has become a recruiter for the terrorist network, feeding prospects into plots aimed at the United States and at Americans abroad, the officials said. It is extremely rare, if not unprecedented, for an American to be approved for targeted killing, officials said. A former senior legal official in the administration of George W. Bush said he did not know of any American who was approved for targeted killing under the former president. But the director of national intelligence, Dennis C. Blair, told a House hearing in February that such a step was possible. 'We take direct actions against terrorists in the intelligence community,' he said. 'If we think that direct action will involve killing an American, we get specific permission to do that.' He did not name al-Awlaki as a target. The step taken against al-Awlaki, which occurred earlier this year, is a vivid illustration of his rise to prominence in the constellation of terrorist leaders. But his popularity as a cleric, whose lectures on Islamic scripture have a large following among English-speaking Muslims, means any action against him could rebound against the United States in the larger ideological campaign against al-Qaida. The possibility that al-Awlaki might be added to the target list was reported by The Los Angeles Times in January, and Reuters reported Tuesday that he was approved for capture or killing. People on the target list are considered to be military enemies of the United States and therefore not subject to the ban on political assassination first approved by President Gerald R. Ford. 