The invention provides a method and a device for amplitude modulation of a radio frequency signal using a variable-gain radio frequency power amplifier, for automatic control of the amplifier output signal by generating an error signal between an amplitude modulation signal and a signal representing the power of the amplifier output signal, from which a gain control signal of the amplifier is generated, to monitor potential saturation of the amplifier by comparing the relative phases of the error signal and of the amplitude modulation signal, and, in case of saturation of the amplifier, to generate a correction signal for lowering the operating point of the amplifier. The invention is applicable to a transmitter of a mobile station or a fixed station of a radio communication system.