We suggest using modulated self-injected radiation to achieve lasing regimes similar to Q-switching in a CO<sub>2</sub> laser without loss of average output power. The feasibility of this solution is verified both theoretically and experimentally. Our theoretical model of CO<sub>2</sub> laser is based on a standard six-temperature model supplemented with terms accounting for self-injection of laser output radiation. We show that temporal modulation of self-injected radiation with power several percent that of the laser output power in external optical systems achieves pulsed-periodical generation regime. The model is experimentally verified using a commercial CO<sub>2</sub> laser. With modulation less than 5% of the output power pulsed-periodical lasing was realized. Pulse duration obtained was 300 ns with repetition rate of 20 kHz and power maximum-to-average rate around 20.