The New York Civil Liberties Union sued the city's police department Thursday, calling the random search of subway riders' bags unconstitutional and ineffective.

The lawsuit -- filed in a federal court on behalf of five subway passengers, including the son of a retired police captain and a naturalized citizen -- alleges that the program violates constitutional rights that protect against illegal searches and guarantee due process.

New York City's transit system is the first in the nation to institute regular, random checks of passenger bags. The searches began July 21, after terrorist suicide bombings two weeks earlier in London's transit system killed 52 bystanders. Critics not aligned with civil liberties activists also say the searches are ineffective but say they want police to begin racial profiling of passengers to emphasize searches of young men of Middle Eastern or Asian descent.

Civil liberties advocates said searches that are not based on suspicion do little to protect the public, particularly when mass-transit riders who refuse to submit to the searches are allowed to enter the subway system at another station.

"People are allowed to walk away, ensuring that only innocent people are searched," said Donna Lieberman, executive director of the NYCLU, who called the searches a "civil liberties surcharge on a Metrocard."

The searches are performed on a rough mathematical formula of one out of five to 10 people depending on foot traffic, according to police officials.

New York subways move 4.7 million passengers, nearly half of the nation's mass-transit riders. New Jersey riders boarding trains to New York recently became subjected to similar searches.

Gail Donoghue, special counsel in the city's legal department, called the NYCLU "shortsighted" and said in a written statement that the program "preserves the important balance between protecting our City and preserving individual rights."

City police officials said they have received no complaints about the policy.

The Supreme Court has approved the use of checkpoints in special circumstances, but in 2000 the court ruled that random searches could not be employed for the "ordinary enterprise of investigating crimes."

A plaintiff in the NYCLU lawsuit, Joseph Gehring Jr., the son of a retired police captain and a "lifelong Republican," said he began avoiding police checkpoints after his bags were searched. "I've been forced to act like a criminal in my own city when I have done nothing wrong," said Gehring, who lamented a lack of opposition by New Yorkers to the program. "We are becoming accustomed to having our liberties taken away."

New York state Assemblyman Dov Hikind (D) plans to introduce legislation in the state legislature within two months that will empower police officers to single out people based on national origin and ethnicity.

"Police officers need to keep specific attention to young people -- Middle Eastern, South Asian -- based on a profile that is so obvious," Hikind said.

New York City Council member James S. Oddo (R) said he will introduce a nonbinding resolution in support of the legislation.

On a Manhattan-bound subway, Princess Alexander, 38, offered her conditional support for the police searches, saying, "This is what we have to live with right now." But Alexander, an office manager, said she is opposed to racial profiling. "We have been singled out," said Alexander, who is black.

Christopher Dunn leads the New York Civil Liberties Union effort to end random searches of riders.