City Council Speaker Christine Quinn issued her sharpest criticism of how the New York Police Department has carried out its stop-and-frisk policy, saying the tactic has sometimes “sown distrust” in minority communities.

In a letter to Commissioner Raymond Kelly, Ms. Quinn acknowledged the practice—in which police stop people on the street and occasionally frisk them—has helped drive down crime rates. But she said police were falling short in several areas and outlined a plan to change the policy.

“I am concerned that a rift has developed between the police department and New Yorkers—particularly New Yorkers of color,” Ms. Quinn’s letter said. “Much of this division is centered around stop, question and frisk practices.”

In her letter, Ms. Quinn, a potential 2013 mayoral candidate, defended stop-and-frisk as a “viable and effective crime fighting tool”—as she has in the past. And she noted that a 51% decrease in murders during the past decade could be attributed, at least in part, to stop-and-frisk.

Still, Ms Quinn wrote, “young men of color consistently report” that they are repeatedly stopped, and some of those encounters result in accusations of excessive force. Allegations that officers are pressured to meet stop-and-frisk quotas are also “troubling,” and the department needs to ensure quotas play “no role,” Ms. Quinn wrote.

In the letter, the speaker calls for improvements in police training, supervision, discipline, monitoring and transparency.

Paul Browne, the NYPD’s chief spokesman, said: “Commissioner Kelly is happy to review suggestions from Speaker Quinn, especially in this instance, where she recognizes the dramatic murder reduction of the last decade and the role police strategies played in it.”

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