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.

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