The system comprises a lever (2) that is rotatable about a point fixed to the vehicle and articulately joined to the upper edge (6) of the leaf (1); a horizontal guide (3) through which a carriage (4) slides; push-pull means (10,11) that articulately link the upper edge (6) to the carriage (4); and actuation means (12) simultaneously linked to the lever (2) and the carriage (4), which are adapted to distribute their action on the lever (2) and the carriage (4) depending on the force to overcome in order to open and close the leaf (1), such that their action is automatically distributed on the lever (2) when greater power is required to move the carriage (4), this is essentially during the initial opening operation from the end closing position, and during the closing and locking operation from an imminent closing position.