B757-200. GND CREW OPERATING AN EXTERNAL AIR STARTER DID NOT KNOW HOW TO SET UP THE STARTER. THE STARTER WOULD NOT ALLOW SUFFICIENT AIRFLOW TO START AN ACFT ENG.

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APU WAS ON A PLACARD. WE HAD TO START AT THE GATE USING EXTERNAL AIR AND ELECTRICAL PWR. PRESSURE WAS OK WHEN WE STARTED THE ENG START SEQUENCE. THE ENG ATTAINED STARTING N2 RPM; BUT ACCELERATED SLOWER THAN NORMAL. HAD TO ABORT THE START DUE TO STARTER ENGAGE TIME LIMIT. FLT ATTENDANTS CALLED TO RPT LOTS OF SMOKE VISIBLE OUT THE WINDOW AND FUMES IN THE CABIN. A TIMELY PA FROM THE COCKPIT REDUCED THE ANXIETY IN THE CABIN. THE FUMES CLRED QUICKLY WHEN THE AIR CONDITIONING PACKS WERE REINSTATED. I INFORMED THE GND MAN THAT WE NEEDED MORE PRESSURE FROM THE START UNIT. AFTER SEVERAL MINS; HE TOLD ME THAT IT SHOULD BE OK NOW. THE SAME PROB OCCURRED WITH FUMES IN THE CABIN. I CALLED FOR MAINT. THEY CORRECTED A VALVE CONFIGN ON THE START CART. IT WORKED FINE AFTER THAT. SEEMS LIKE SOME TRAINING IS NEEDED IN LGA. MY PAX ALMOST DEPLOYED THE SLIDES AND JUMPED OUT ON THE RAMP BECAUSE OF OPERATOR ERROR. I AM ALSO CONCERNED THAT THE GND MAN AT NO TIME TOLD US ABOUT THE EXCESSIVE SMOKE DURING ENG START.