As the Police Department’s stop-and-frisk practice draws increasing criticism from black and Latino New Yorkers, the city’s public advocate, Bill de Blasio, said he would call on the mayor to force a reduction of the controversial practice.

The proposal, which Mr. de Blasio plans to announce on Wednesday, comes as the stop-and-frisk tactic has emerged as the first major contentious issue of next year’s mayoral race. Mr. de Blasio, who is expected to be a candidate, has been among the most outspoken on the topic among the possible Democratic contenders.

The issue holds great significance for the left-leaning and black and Latino voters who can often sway the outcome of the Democratic mayoral primary. But polls suggest that many New Yorkers support the policy, believing it makes the city safer.

On Tuesday, one of Mr. de Blasio’s likely opponents, the City Council speaker, Christine C. Quinn, offered a more measured critique of the practice while she was at a news conference with Raymond W. Kelly, the police commissioner.