A senior Bronx prosecutor was demoted — and her pay cut by $5,000 — because she flubbed the case of a parolee accused of trying to kill a cop.

Christine Scaccia, a 20-year veteran of the Bronx District Attorney’s Office who held the lofty title “director of gang prosecutions,” will also be docked two weeks’ pay, a spokeswoman for District Attorney Robert Johnson said yesterday.

Scaccia will stay with the Gang Prosecution/Major Case Bureau, but as a senior trial attorney earning $130,000 a year, $5,000 less than she earned as a superviseor.