JetBlue became the first airline to install tiny cameras in a passenger cabin. Most other American airlines are expected to follow in short order.

"The cabin camera surveillance system is the logical next step to protect our customers and crew," said David Neeleman, JetBlue's chief executive.

The hidden cameras will allow pilots to watch passengers on two cockpit screens. "If there was a disturbance back there," said Captain Lanny McAndrew, chief pilot for JetBlue, "they would be able to monitor the situation and land as soon as possible."

But Mitch Dresner, a New York business executive who is also a frequent flier, says the benefit of camera surveillance is not worth the intrusion. "I don't think it will make a difference," Mr. Dresner said. "The pilots have enough to do. It won't stop anybody from getting on the aircraft."

Putting cameras on board aircraft was a recommendation of a committee of airline industry executives and government officials after the Sept. 11 terrorist attacks. While there is no legal requirement to do so, 19 other airlines have already applied to the Federal Aviation Administration for permission to introduce the surveillance equipment on both domestic and international flights. The F.A.A. refused to say which airlines had applied.

But critics, while agreeing that surveillance cameras may provide added security, want assurances that passenger privacy rights will be protected.

"We do have privacy concerns," said Barry Steinhardt, associate director of the American Civil Liberties Union. "This is an example of where technology is in the Space Age, but the law that protects privacy is back in the Stone Age. This may well be an appropriate role, but we don't know if it will be abused in the future."

Under pressure to put security measures in place as quickly as possible, the airlines are rushing to put cameras or other alarm devices on board. JetBlue was the first to get official permission from the F.A.A.; it has installed cameras in one plane and plans to add them to the rest of its fleet over the next three months.

Delta Air Lines (news/quote) received F.A.A. approval last October to test security cameras on one of its jetliners. "We are currently evaluating the results of that test," said Katherine Stengel, a spokeswoman for Delta. "We are looking at different products to enhance security on our aircraft."

United Airlines, a unit of UAL (news/quote), also confirmed that it had applied for authority to install security cameras. "We are looking at multiple cameras outside the cockpit door," said Joe Hopkins, a spokesman for the airline. AMR's American Airlines said it was looking at a variety of ways to monitor its cabins.

The airlines' applications will be approved "as soon as possible," said Paul Takemoto, a spokesman for the F.A.A. "We are interested in anything that might improve onboard security. We are also pleased to see the airlines are moving quickly ahead to take the additional security steps called for by the president."

The added security does not come cheaply. For JetBlue, adding the surveillance cameras, which are made by AD Aerospace of Washington and being installed by LiveTV of Melbourne, Fla., will cost about $50,000 for each of its 24 Airbus jetliners. New aircraft added to the fleet will come with the cameras already installed.

Putting cameras in passenger cabins has widespread support from industry groups.

"The flight deck crew members should have the ability to monitor activities in the cabin since cockpit doors have been fortified, and pilots are expected to remain in the cockpit," said Michael Wascom, a spokesman for the Air Transport Association in Washington. "Clearly the concept has our support as a security tool."

A coalition of airline leaders appointed by the Transportation Department in October urged airlines to install security cameras and improve lighting near cockpit doors.

Pilots also like the idea. "We have advocated the idea of having some way for pilots to have some means to see what is going on," said John Major, a spokesman for the Air Line Pilots Association. "Its only purpose is to serve security. It should not be recording."

Mike Home, managing director for AD Aerospace, echoed that point, but argued that recording the images should not be ruled out. Pilots will be able to "make informed decisions regarding actions or diversions, without putting themselves and the aircraft in danger by entering the passenger cabin," he said.

He said that equipment could be installed on any airline that wanted it. That would be an advantage, he said, in verifying any onboard terrorist or prosecuting any passenger who attacks someone on board.

Mr. Neeleman, JetBlue's chief executive, emphasized that video pictures on its airliners would not be recorded, and that no cameras would be installed in the bathrooms. "Passengers are informed about the cabin cameras at the beginning of each flight as part of the in-flight safety announcements," he said.

According to Glenn Latta, executive vice president of LiveTV, the cameras will still be rolling at night during overnight stops, and pictures sent by a wireless device on the aircraft will allow security agents to monitor maintenance workers and employees of outside suppliers who board an aircraft.

Mr. Home of AD Aerospace said, "Live pictures generated on board the aircraft while it is parked at the gate can become an integrated part of the airport video security system."