"If I can just get in there and get information off the ground, I might find one piece of information that's going to lead me to the prize," the former official said.
The broader dimensions of the program may account for why some lawmakers, particularly Republicans, have been critical of CIA Director Leon E. Panetta's decision last month to kill it.
House Democrats, angry that the program was kept secret from Congress, at least partially at the urging of former Vice President Dick Cheney, have threatened an investigation.
Lawmakers on Wednesday continued sparring over Cheney's role and whether Congress had been properly briefed.
The CIA said the program was never of substantial value to U.S. efforts.
"The program [Panetta] killed was never fully operational and never took a single terrorist off the battlefield," said George Little, a CIA spokesman. "We've had a string of successes against Al Qaeda and other terrorist groups, and that program didn't contribute to any of them."
The broader objectives of the program may also help to explain why top counter-terrorism officials saw a need for the CIA to develop its own elite paramilitary teams, rather than relying on U.S. military special operations troops deployed across Afghanistan.
Former intelligence officials said there were intermittent discussions about having special operations troops assigned to the CIA as part of the program, but it was not clear how far those plans progressed.
A second former official with extensive knowledge of the CIA effort said it was seen as crucial that the units reside within the CIA so that the U.S. government would be able to deny involvement if a team were exposed or captured.
Special operations forces routinely carry out clandestine missions, but unlike their CIA counterparts they operate with the expectation that their ties to the U.S. government will not be denied if the mission breaks down.
"Keeping activities like this secret is the biggest challenge," said the second former U.S. intelligence official.
The vulnerability of being far removed from U.S. protection was seen as another major barrier to the success of the program.
Even if an assassination team were deployed and succeeded in killing a senior Al Qaeda figure, "what happens to the shooter?" said Mark Lowenthal, a former senior CIA official. "We don't send people on suicide missions. I'm sure they were troubled by how to get the guy out of there."
