Activists see the potential for unconstitutional invasions of privacy and for database mix-ups that could lead to innocent people being branded security risks.
"This system threatens to create a permanent blacklisted underclass of Americans who cannot travel freely," said Katie Corrigan, a lawyer for the American Civil Liberties Union.
There also is concern that the government is developing the system without revealing how information will be gathered and how long it will be kept.
The system, ordered by Congress after the Sept. 11 attacks, will gather much more information on passengers than has been done previously. Delta Air Lines will try it out at three undisclosed airports beginning next month, and a comprehensive system could be in place by the end of the year.
Transportation officials say a contractor will be picked soon to build the nationwide computer system, which will check such things as credit reports and bank account activity and compare passenger names with those on government watch lists.
Advocates say the system will weed out dangerous people while ensuring law-abiding citizens aren't given unnecessary scrutiny.
Transportation officials say CAPPS II — Computer Assisted Passenger Prescreening System — will use databases that already operate in line with privacy laws and won't profile based on race, religion or ethnicity.
"What it does is have very fast access to existing databases so we can quickly validate the person's identity," Transportation Secretary Norman Mineta said.
An oversight panel, which will include a member of the public, is being formed. The Transportation Security Administration will set up procedures to resolve complaints by people who say they don't belong on the watch lists.
Transportation Department spokesman Chet Lunner said a Federal Register notice saying the background information will be stored for 50 years is inaccurate. He said such information will be held only for people deemed security risks.
Jay Stanley, an ACLU spokesman, was skeptical.
"When it says in print, 50 years, we'd like to see something else in print to counter that," he said.
Airlines already do rudimentary checks of passenger information, such as method of payment, address and date the ticket was reserved. The system was developed by Northwest Airlines in the early 1990s to spot possible hijackers.
Unusual behavior, such as purchasing a one-way ticket with cash, is supposed to prompt increased scrutiny at the airport.
Capt. Steve Luckey, an airline pilot who helped develop the system, said CAPPS II will help discern a passenger's possible intentions before he gets on a plane.
Unlike the current system, in which data stays with the airlines' reservation systems, the new setup will be managed by TSA. Only government officials with proper security clearance will be able to use it.
CAPPS II will collect data and rate each passenger's risk potential according to a three-color system: green, yellow, red. When travelers check in, their names will be punched into the system and their boarding passes encrypted with the ranking. TSA screeners will check the passes at checkpoints.
The vast majority of passengers will be rated green and won't be subjected to anything more than normal checks, while yellow will get extra screening and red won't fly.
Paul Hudson, executive director of the Aviation Consumer Action Project, which advocates airline safety and security, is skeptical the system will work.
"The whole track record of profiling is a very poor to mixed one," Hudson said, noting incorrect profiles of the Unabomber and the Washington-area snipers.
Nine to 11 of the 19 hijackers on Sept. 11 were flagged by the original CAPPS, but weren't searched because the system gave a pass to passengers who didn't check their bags, Hudson said. People without checked bags are now included.
CAPPS II is one of at least two efforts by the federal government to develop new technology for detecting potentially dangerous patterns of behavior.
The other is the Total Information Awareness program being developed by the Pentagon, which aims to mine and associate electronic data to identify possible security threats.