Police Work: Getting Past Raw Emotion
Clyde Haberman, in NYC column, holds that Rev Al Sharpton got debate between Democratic presidential candidates Al Gore and Bill Bradley off to interesting start when he asked them how they would keep crime down and at same time confront problem of police brutality; maintains that his question struck certain balance not often evident in last year of tears and rage over Amadou Diallo killing; notes that many New Yorkers are accusing Bronx Dist Atty Robert T Johnson of having lost his balance in bringing murder charges against four police officers who shot Diallo (M)