The homeland security bill signed into law yesterday mandates that training begin by the end of February for commercial airline pilots who want to carry firearms in the cockpit. But a key adviser to the program predicts that far fewer than the estimated 30,000 eligible pilots will sign up.

Pilots lobbied aggressively for the right to carry guns after the Sept. 11 terrorist attacks last year. Many of the major airlines opposed the idea, however, so pilots must pay for the training themselves and arrange for training on their own time.

"This is more than lining up the front sight with the rear sight and squeezing the trigger," said Thomas Quinn, director of the nation's air marshal program and a key adviser to the Transportation Security Administration's program for arming pilots. He said pilot training is likely to be more extensive than the 48 hours some pilots would like.

Pilots "have to understand when it's appropriate" to use force, said Quinn, who was directed by TSA chief James M. Loy to provide suggestions this past summer for how to go about arming pilots. "It's policy and guidelines. It's much more difficult than learning to shoot; it's learning when to shoot and when not to shoot."

Quinn did not want to estimate how many pilots would sign up. "What you're going to find is there may not be as many volunteers as may have been suggested," he said.

The TSA, the agency in charge of airport security, is scheduled to move out of the Transportation Department and into the new Homeland Security Department as part of the law signed yesterday. The TSA is charged with developing a program to train pilots even though Loy, who heads the agency, opposes the idea.

Several organizations representing thousands of airline pilots have already started to collect names on sign-up lists. Stephen A. Luckey, chairman of a national security committee at the Air Line Pilots Association, the nation's largest pilots union, said his organization has already suggested that TSA begin training pilots in groups of 50 and that those with the most military or law enforcement experience go first.

Luckey suggested to the TSA that pilots receive 48 hours of training, a figure that Quinn dismissed as "marginal," but Luckey agreed that the agency should not give a gun to every pilot who wants one.

Luckey also agreed that the number of pilots who sign up for the program could be several thousand below the estimated 30,000. "Pilots have a pretty nice life. If you have a weapon, you can't have a glass of wine with dinner, you have to take care of [the gun]. It's not fun.," he said. "Once people realize what's required in order to do this, it's almost like having another job."

The TSA has yet to settle on a number of details in the program, including how much initial and follow-up training pilots should have. The agency also has yet to work out international legal agreements to allow pilots to carry guns into airports of countries that prohibit firearms.

The new law requires the TSA to train pilots as "federal flight deck officers," with training similar to federal agents and the capability to make arrests.

Yesterday, Quinn dismissed the idea advanced by some that pilots be trained at FBI facilities. Most likely, he said, pilots could be trained at TSA facilities used by federal air marshals; the agency also has discussed the possibility of using the federal law enforcement training centers in Georgia and New Mexico.

"The FBI is not needed to do this training," Quinn said. "It's clearly a TSA responsibility."