“I also conclude that the city’s highest officials have turned a blind eye to the evidence that officers are conducting stops in a racially discriminatory manner,” she wrote, citing statements that Mr. Bloomberg and the police commissioner, Raymond W. Kelly, have made in defending the policy.

Judge Scheindlin ordered a number of remedies, including a pilot program in which officers in at least five precincts across the city will wear cameras on their bodies to record street encounters. She also ordered a “joint remedial process” — in essence, a series of community meetings — to solicit public comments on how to reform the department’s tactics.

The judge named Peter L. Zimroth, a partner in Arnold & Porter L.L.P., and a former corporation counsel and prosecutor in the Manhattan district attorney’s office, to monitor the Police Department’s compliance with the United States Constitution. The installation of a monitor will leave the department under a degree of judicial control that is certain to shape the policing strategies under the next mayor.

Judge Scheindlin’s decision grapples with the legacy of Terry v. Ohio, a 1968 ruling by the Supreme Court, which held that stopping and frisking was constitutionally permissible under certain conditions. But she said that changes to the way the New York Police Department employed the practice were needed to ensure that the street stops were carried out in a manner that “protects the rights and liberties of all New Yorkers, while still providing much needed police protection.”

The judge found that the New York police were too quick to deem suspicious behavior that was perfectly innocent, in effect watering down the legal standard required for a stop.

“Blacks are likely targeted for stops based on a lesser degree of objectively founded suspicion than whites,” she wrote.