A kinetic model is developed of a pulse-periodic waveguide CO2 laser excited by a nonautonomous discharge in which the gas is preionized by short high-voltage pulses. The model is used to justify the feasibility of rectangular radiation pulses of 10–30 μsec duration and a repertition frequency 15–50 kHz by dynamic control of the waveguide cavity Q through parabolic variation, in synchronism with the preionization pulse, of the time variation of the output mirror reflection coefficient. In particular, it is shown by numerical simulation that the average lasing power in a meander regime at 50-kHz frequency can exceed 30 W. Perfectly realistic methods of controlling both the cavity Q and the exciting discharge are considered.