DURING A NIGHT APPROACH TO A FIELD ESTABLISHED BY THE LOCAL FIRE DEP'T FOR A MED-EVAC, THE PILOT WAS TOLD OF WIRES ON THE WEST SIDE & THAT ONE OF THE POLICE CARS WAS PARKED BENEATH THEM. HE CIRCLED THE AREA 3-4 TIMES FOR HAZARDS USING THE SEARCHLIGHT WHILE COMMUNICATING WITH GROUND UNITS. AFTER LOADING THE PATIENT THE HELICOPTER DEPARTED TO THE WEST ACROSS THE APRX 500-FT FIELD. WITNESSES STATED THE HELICOPTER NEVER GOT HIGHER THAN THE WIRES UNTIL IT WAS ABOUT 20 FT FROM THEM, THEN NOSE UP TO ABOUT A 45-DEG ANGLE, CLIMB OVER THE WIRES, AND DESCEND INTO THE GROUND. THE ACTING COMMANDER OF THE STATE POLICE AVIATION DIVISION STATED THAT THE USE OF MAXIMUM PERFORMANCE TAKEOFFS IS CONSIDERED MANDATORY WHEN DEPARTING LANDING SITES AT NIGHT WHERE OBSTACLES SUCH AS WIRES ARE IN THE AREA AND THE CREW HAS NEVER LANDED THERE BEFORE.