The method according to the invention is implemented in an alternator-starter (1) comprising phase windings (u, v, w) connected to an inverter (3) linked to an onboard electrical network (2) powered by a battery for operation as a starter. The invention involves controlling the inverter in a chopped full-wave control mode when the rotational speed ([Omega]) of the alternator-starter is lower than at least a threshold speed and in a full-wave control mode when the rotational speed is higher than the threshold speed. According to a specific embodiment, the switching between the chopped full-wave control mode and the full-wave control mode takes place according to a hysteresis cycle using two predefined threshold speeds.