MINNEAPOLIS - Six Muslim men removed from a plane last fall after being accused of suspicious behavior are suing the airline and threatening to sue the passengers who complained - a move some fear could discourage travelers from speaking up when they see something unusual.

The civil rights lawsuit, filed earlier this month, has so alarmed some lawyers that they are offering to defend the unnamed "John Doe" passengers listed as "possible defendants" free of charge. They say it is vital that the flying public be able to report suspicious behavior without fear of being dragged into court.

"When you drive up the road towards the airport, there's a big road sign that says, 'Report suspicious behavior,'" said Gerry Nolting, a Minneapolis lawyer. "There's no disclaimer that adds, 'But beware if you do that, you might get sued.'"

The six imams were taken off a Phoenix-bound US Airways flight on Nov. 20 while returning home from a conference of Islamic clerics in Minneapolis.

Other passengers had gotten nervous when the men were seen praying and chanting in Arabic as they waited to board. Some passengers also said that the men spoke of Saddam Hussein and cursed the United States; that they requested seat belt extenders with heavy buckles and stowed them under their seats; that they were moving about and conferring with each other during boarding; and that they sat separately in seats scattered through the cabin.

The plane was cleared for a security sweep, nothing was found, and the jet took off without the imams.

The Muslim clerics say they were humiliated, and are seeking unspecified damages from the airline, the Minneapolis airport and, potentially, the John Does.

Omar Mohammedi, the New York City attorney for the imams, said the intent is not to go after passengers who raise valid concerns about security. But he suggested some passengers may have acted in bad faith out of prejudice.

"As an attorney, I have seen a lot of abuse by the general public when it comes to members of the community creating stories that do not exist," Mohammedi said.

He denied the imams were talking about Saddam, and said that their seats were assigned and that they requested extenders because their seat belts didn't fit.

Some fear such lawsuits could weaken what has become the first line of defense against terrorism since Sept. 11 _ an alert public. At airports and train and subway stations around the country, travelers are routinely warned to watch for unattended bags and suspicious activity and to notify authorities.

Ellen Howe, spokeswoman for the Transportation Security Administration, which oversees security at all U.S. airports, would not comment specifically on the imams' lawsuit. But she said the TSA counts on passengers to help the agency do its job.

"'See something, say something' is certainly a common mantra in this day and age," Howe said. "We would always remind passengers to be both vigilant and thoughtful."

In reaction to the imams' lawsuit, Congress has taken steps to legally protect passengers who report suspicious activity. Earlier this week, the House approved an amendment to a rail transportation security bill that would make passengers immune from such lawsuits, unless they say something they know is false.

Mohammedi said he has not yet identified any of the complaining passengers. An airport police report listed a passenger and two US Airways employees as complaining about the imams. All three had their names blacked out before the lawsuit was filed by invoking a Minnesota law that allows it, airport spokesman Pat Hogan said.

Nolting said he has been contacted by several potential John Does.

Passenger Pat Snelson, who lives in a Twin Cities suburb, said he and his wife were not among those who reported suspicious behavior. But he said his wife noticed the men praying, and he saw them moving around the cabin while others were boarding.

"These guys were up to no good," Snelson said. "We think the airport people did a real good job in taking care of it."

Bomb-sniffing dogs examined the men and their baggage. FBI agents and other federal law enforcement officers questioned the men for several hours before releasing them.

Billie Vincent, a former director of security for the Federal Aviation Administration, said he is troubled by the mere attempt to identify the passengers who raised concerns.

Airline passengers "are your eyes and your ears," said Vincent, who now owns an aviation security company. "If attorneys can get those names and sue them, you put a chilling effect on the whole system."

(A previous version of this story said the passengers were defendants in the lawsuit. They are not. The lawsuit cites passengers as "possible defendants.")