The control system comprises: a first hydraulically-operated actuator device for controlling the engagement of a first set of gears by selection and engagement movements; a second hydraulically-operated actuator device for controlling the engagement of a second set of gears by selection and engagement movements; a first solenoid valve of the ON/OFF type arranged to put the first or the second actuator device alternatively into communication with a supply of fluid under pressure; a second solenoid valve of the ON/OFF type arranged to control the selection movements of the actuator device which from time to time is in communication with the fluid supply; a distributor interposed between the fluid supply and the two actuator devices and displaceable under the control of the first solenoid valve between a first working position in which it puts the fluid supply into communication with the first actuator device and a second working position in which it puts the fluid supply into communication with the second actuator device; a third proportional pressure solenoid valve and a fourth proportional pressure solenoid valve arranged to control the engagement movements of the actuator device which from time to time is in communication with the fluid supply. With such a control system the gear change operation thus requires the intervention of at most four solenoid valves.