The official in charge of fighting racial profiling for the American Civil Liberties Union says he was the victim of profiling at Logan Airport, and he has gone to federal court to challenge a screening technique that relies on suspicious behavior to identify potential terrorists.

King Downing said he was stopped and questioned by State Police in October 2003 after arriving on a flight to attend a meeting on racial profiling.

Downing sued the Massachusetts Port Authority, which operates the airport, and Massachusetts State Police, alleging they violated his constitutional right against unreasonable search. A trial began yesterday in US District Court.

Downing, who is black and wears a short beard, said in his lawsuit that he was stopped by a state trooper and asked to show identification after he left the gate area and made a phone call in the terminal.

When he declined, Downing said, he was told to leave the airport, but was then stopped again. He was surrounded by four state troopers and told he was under arrest for not failing to produce identification.

Downing, an attorney who serves as national coordinator of the ACLU's Campaign Against Racial Profiling, said that after he agreed to show his driver's license, the troopers asked to see his airline ticket. He was then allowed to leave, and no charges were filed against him.

In his lawsuit, Downing alleges the behavioral screening system at Logan International Airport encourages racial profiling. His lawsuit seeks unspecified damages and a ruling to declare the screening system unconstitutional.

Downing was stopped "for no apparent reasons other than his appearance," said Peter Krupp, one of his attorneys. "He knew his rights, and he knew he had done nothing wrong."

In 2002, about a year after terrorists launched the Sept. 11 attacks by hijacking two planes from Logan, the airport became the first in the country to use a program called the Behavior Assessment Screening System, in which police question passengers whose behavior appears suspicious.

The Transportation Security Administration has rolled out a similar system at more than 40 of the nation's largest airports. Officials at Logan have previously said suspicious activity includes loitering without luggage, wearing heavy clothes on a hot day, and watching security methods.

Logan officials say race played no role in the decision to question Downing. The first trooper to ask him for identification was black, and three of the four officers who arrived later also were black, court documents indicated. The first trooper said he became suspicious when he saw Downing watching him.

Airport officials said behavior-pattern recognition helps strengthen security and does not involve racial profiling.

"We welcome the opportunity to defend the program in court," said Matthew Brelis, a spokesman for Massport.

© Copyright 2007 Globe Newspaper Company.