SF340 First Officer reports Left Bleed Air Leak caution message approaching 6000 FT during climb. QRH procedures were complied with; which resulted in an engine shutdown and return to departure airport.

Narrative

Just prior to level off at Cruise (6000 FT) we received a Master Caution; Left Air Leak. The Captain was pilot flying; I identified the Caution; Left Air Leak and noted the L bleed valve had closed. Captain maintained pilot flying and I handed off the radios to him while I ran the Non-Normal checklist for the annunciation. The checklist had us reset the bleed and HP bleed in an attempt to extinguish the light. The checklist was performed twice as directed by the QRH; but was unsuccessful in extinguishing the Left Air Leak light. The QRH then directs the crew to shutdown the affected engine. At this point I took over as pilot flying and radio 1 in touch with ATC; while the Captain notified the flight attendants and dispatch. I set up for Runway XX and requested ATC for vectors as well as notified them of a possible emergency landing. Shortly afterwards I returned pilot flying duties and both radios to the Captain while I ran the emergency Non-Normal checklist for engine shutdown. I monitored ATC communication and flight instruments for correct set up. The crew stayed calm and collected throughout the flight and landed without incident. The passengers were informed of the situation and deplaned under normal conditions into the terminal. The flight was subsequently canceled and maintenance notified through dispatch. After reviewing with maintenance the following day; they explained to me that they believed the bleed air leak detector loop was faulty; and subsequently replaced. The crew repositioned the aircraft without further incident.