NEW YORK — The New York Police Department deliberately violated the civil rights of tens of thousands of New Yorkers with its contentious stop-and-frisk policy, and an independent monitor is needed to oversee major changes, a federal judge ruled today in a stinging rebuke for what the mayor and police commissioner have defended as a life-saving, crime-fighting tool.

U.S. District Court Judge Shira Scheindlin said she was not putting an end to the policy, but rather was reforming it. She did not give specifics on how that would work but instead named an independent monitor who would develop reforms to policies, training, supervision, monitoring and discipline.

“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.

“In their zeal to defend a policy that they believe to be effective, they have willfully ignored overwhelming proof that the policy of targeting ‘the right people’ is racially discriminatory.”