But even if alternative bases are secured, the officials said, the CIA’s capability to gather sufficient intelligence to find al-Qaida operatives and quickly launch drone missiles at specific targets in Pakistan’s mountainous tribal region will be greatly diminished if the spy agency loses its drone bases in Afghanistan.

The CIA’s targeted killing program thus may prove a casualty of the bitter standoff with Afghan President Hamid Karzai over whether any U.S. troops can remain in Afghanistan after 2014, as the White House has sought. Karzai has refused to sign a bilateral security agreement to permit a long-term American deployment, and some White House aides are arguing for a complete pullout.

According to current and former officers, CIA analysts operating from fortified outposts near the Pakistani border evaluate electronic intelligence, while case officers meet sources who help them identify targets. They pay people to place GPS trackers on cars or buildings to help guide the drone-launched missiles.

The CIA cannot fly drones from its Afghan drone bases without U.S. military protection, according to several American officials who spoke on condition of anonymity because the program is classified. If the bases are evacuated, the CIA fleet of armed Predator and Reaper drones could be moved to air fields north of Afghanistan, U.S. officials say, without naming the countries.

The CIA and the military used an air base in Uzbekistan to conduct drone flights until the U.S. was evicted in 2005, said Brian Glyn Williams, a University of Massachusetts professor and author of the book, “Predators: The CIA’s Drone War on Al Qaeda.”

The military also has used a base in Kyrgyzstan to conduct air operations, including moving troops and supplies into Afghanistan. The Pentagon announced last fall that it would shift those operations to Romania this summer.

Officials say a new jet-powered drone, called the Predator C, or Avenger, could figure in plans to use bases outside Afghanistan. The Avenger could “get to ‘hot’ targets in Pakistan much faster and might solve some of these logistic problems posed by the slower-moving, propeller-driven Predator and Reaper drones,” said Williams, the professor.

General Atomics, which makes the Avenger, says it is ready for combat. So far, the San Diego-based company has built four prototypes.