Workers at J.F.K. say security inspections are rushed. Mohamed, an airport security worker for Global Elite Group, said a focus on speed is jeopardizing passenger safety. After passengers exit each plane at John F. Kennedy International Airport, squads of caterers and cleaners troop on and prepare the aircraft for the next flight. Once cleared of crumbs and discarded magazines, each empty plane gets another sort of once-over, this time from a crew of security agents who, as part of federally mandated security measures, conduct a search of every cabin for items left behind, including weapons, explosives and drugs. They are supposed to open every overhead bin, flip down each tray table and probe all the seat-back pockets, one by one.But at Kennedy, one of the world’s busiest airports, these inspections are up against efforts to avoid delaying flights. Some checks that should take hours are done in mere minutes — sometimes as many as half the seats on a jetliner are skipped altogether — according to a group of the privately contracted security employees who conduct the inspections.