American officials are considering expanding the targeted killing program in Yemen as terror groups there are strengthening their ties to militants in Pakistan and the Horn of Africa. The change would give the C.I.A. a much larger role in the secret military campaign there, one modeled on the campaign of drone attacks in Pakistan. The C.I.A. and the military’s Special Operation Forces have been putting personnel, drones, and surveillance equipment into place in Yemen, as well as Kenya, Djibouti, and Ethiopia, to ready for more attacks against al Qaeda in the Arabian Peninsula, the Yemeni affiliate of al Qaeda, and Somalia’s al Shabaab, which has been fighting to topple the Somali government for years. Those groups are believed to be working closer together toward plotting attacks against the U.S. Those groups pose a greater threat, some officials think, than the al Qaeda leaders who plotted 9/11 but are now hiding in Pakistan. The Yemeni group has been savvy in recruiting people who understand the U.S., as with Fort Hood shooter Maj. Nidal Hasan.