Having your name added to the Transportation Security Administration's watch list, a register of airline passengers the government wants to screen more rigorously, is easy.
Just ask Harold Smith, who works for a specialty surgical-equipment distributor in Fort Worth. One recent morning, as he checked in for a flight to Austin, Tex., an electronic kiosk rejected his seat assignment request and referred him to the ticket counter.
An airline employee quietly told him he was ''watch-listed'' and could only board after law enforcement authorities were called. ''I have no idea how my name got on that list,'' said Mr. Smith, who describes himself as an average-looking grandfather with a clean record. He was allowed to check in after a brief wait.
Having your name taken off the security administration's watch list, however, is not so easy. For three weeks, after being stopped every time he tried to board a flight, Mr. Smith said he begged airline workers and administration agents for help clearing his name. ''The T.S.A. agents I spoke with didn't know what to do, and they couldn't tell me who the ranking officer was,'' he recalled.
Finally, a sympathetic airline worker offered him a phone number for the administration's ombudsman, its passenger advocate. The watch list is a generic term for at least nine government databases estimated to include more than 40,000 names. The names are divided into a no-fly list of a few thousand people suspected of terrorist activity or believed to be a threat to national security and a much larger list of ''selectees'' who are required to be questioned by the security administration before boarding.
Despite its size, that second database remains something of a mystery. According to people with access to it, air travelers can be put into it for activities like paying for a ticket with cash, booking a seat at the last minute, flying one way instead of round trip and even arriving at the airport without luggage.
There is no way to find out if you are on the list until you check in for a flight. Worse, there may be no way off. Passengers can fill out a disparity claim with the ombudsman's office, which acts as an intermediary between passengers like Mr. Smith and the security agency. ''If it's determined that you're not the individual that is wanted for further questioning, then the airlines will receive notification informing them that the specific individual is not to be detained,'' a T.S.A. spokeswoman, Lauren Stover, said.
But that does not mean they are off the watch list. The agency's Office of Intelligence, which currently maintains the watch list, reports that in September, 680 people filed so-called disparity claims indicating that their names had been mistaken for individuals wanted by the government for questioning. Of those, the government had cleared 250 people by October.
All that apparently means, however, is that their identities had been clarified to prevent ''false positives;'' the names are not necessarily removed from the databases. In some cases, the agency does delete a person from the list after a waiting period, but it will not say how long it takes or what the criteria are. Nor will it disclose the success rate of passengers whose names are added to the lists for legitimate reasons or their chances of having their names cleared.
Mr. Smith is still waiting to find out his exact status. More than a month after he was tagged, the security administration e-mailed him a Passenger Identity Verification Form requesting copies of his driver's license number and voter registration card or military discharge papers, as well as his height, weight and eye color. He filled out the form and returned it within a day, but has not heard from the agency since. Then again, he is no longer being stopped at the airport, and says he expects to be notified soon that he has been cleared.
What if the government decides that a traveler has not been misidentified and belongs on its watch list? According to the agency, there is no formal appeals process. Travelers can either accept the decision or, as a last resort, sue the government.
That is exactly what several travelers did in April, when they filed a class-action challenge to the watch list with the assistance of the American Civil Liberties Union. The A.C.L.U.'s lead lawyer in the case, Reginald Shuford, said airline passengers were being subjected to repeated delays or detentions and had ''no way to clear their names.''
Mr. Shuford said the watch list violated passengers' constitutional rights. ''There's no mechanism in place that would allow travelers to avoid the repeated humiliation of being singled out as a suspect when they try to fly,'' he said. ''The watch list is a complete mess. Its purpose may be laudable, but the way it's currently administered and maintained does not achieve its purpose.''
Critics of the current screening system agree that the watch list is defective and that frequent travelers are suffering because of it. ''The list is obsolete,'' said Richard Eastman, a technology consultant in Newport Beach, Calif. ''There are more efficient ways of finding a threat.''
He suggested that a smarter way to catch suspicious passengers would be to identify them before check-in, which was the idea behind Capps II, a proposal to prescreen airline passengers that has been abandoned, and its successor, a modified concept called Secure Flight. Under the new program, the responsibility for checking airline passengers' names against the watch lists will shift from the airlines to the security agency, which the agency says will eliminate most of the false alerts caused by what it calls the ''current outdated system.''
Detractors also maintain that the secrecy shrouding the watch list is pointless. ''How do you get on the list?'' asked Edward Hasbrouck, a privacy advocate in San Francisco. ''Nobody knows. How do you get off the list? Nobody knows.''
Ms. Stover of the security administration said passengers were added to the secondary list if there was ''a pattern in something they have done in the past that merits future scrutiny,'' and were put on the no-fly list only if they were wanted ''for activities that may be terrorist-related or pose a threat to national security.'' She declined to elaborate.
But Mr. Hasbrouck said even if the government could successfully argue for keeping its reasons secret -- and he doubted it could -- there were still no legal safeguards to prevent innocent passengers from being erroneously added to the watch list. ''The model is flawed,'' he said. ''People should only be placed on the list based on an order from a court of competent jurisdiction following an adversarial evidentiary hearing. The burden of proof should be on the government to show that someone is dangerous, not the other way around.''
He is hardly the only one frustrated by the lists. Frequent travelers like Heather Marie Owens, a corporate travel agent in Norfolk, Va., are so fatigued by their watch-list problems that they have resorted to extraordinary measures.
''On every recent flight I have flown on since November 2001, they tell me I'm on a watch list,'' she said. ''When I ask why, they say it's random. But I don't believe them anymore.''
Ms. Owens said she had endured increasingly humiliating searches by security screeners and had experienced a range of emotions from bewilderment and helplessness to, finally, resignation. On her next trip to Miami, she is bypassing the security agency altogether.
''This time,'' she said, ''I'm driving.''