By Michael Sauter
Updated April 23, 1999 at 04:00 AM EDT

Ted Demme’s Monument Ave., a raffish portrait of small-time crooks, starts out like an Irish Mean Streets. Then two gunshots in a barroom shift the mood, with shocking suddenness. After that, the film belongs to a car thief (Denis Leary) whose fealty to his boss (Colm Meaney) is fading fast. It’s not just because his cousins are getting whacked to enforce a code of silence, or even that the woman he loves (Famke Janssen) now belongs to the boss; it’s his deepening moral confusion as he gets dragged deeper into Mob hierarchy. Monument Ave. depicts this tribe of thieves as a cancer infecting the ethnic roots of a Boston neighborhood, but even more disturbing is its vision of a parochial world so blighted by poverty, racism, and violence that the Mob seems like a natural outgrowth. Few streets have seemed meaner. A-