Security at Logan International Airport, praised for its overhaul after Sept. 11, 2001, has come under fire for a technique that allows police to stop and question people they believe are behaving suspiciously.

The American Civil Liberties Union filed a lawsuit Wednesday challenging the "behavior pattern recognition" program at Logan -- from which two planes were hijacked and crashed into the World Trade Center -- saying it "effectively condones and encourages" racial and ethnic profiling.

The lawsuit was filed on behalf of King Downing, the ACLU's national coordinator for racial profiling, who alleged he was harassed by state police last year. It seeks unspecified monetary damages and asks the court to declare the screening system unconstitutional.

"This program is another unfortunate example of the extent to which we are being asked to surrender basic freedoms in the name of security," said John Reinstein, legal director of the ACLU's Massachusetts chapter. "This allows the police to stop anyone, anytime, for any reason."

State police insist they focus on travelers' behavior, including loitering without luggage, wearing heavy clothes on a hot day and watching security methods at the airport.

George N. Naccara, the federal security director at Logan under the Transportation Security Administration, said troopers are trained not to stop people based on race or ethnicity. "They make it very clear in the training that we're looking for abnormalities in behavior, and they begin their thought process very carefully," Naccara said.