A frequency selected (FS) Q-switched (QS) e-beam controlled-discharge (EBCD) CO-laser has been researched and developed. The laser generates short pulses ((tau) out approximately 1 - 10 microsecond(s) ) having different spectral contents including single line one within 4.95 - 6.50 micrometers spectral range. A special optical scheme has been chosen, which has enabled us to study an influence of spectral contents of CO laser radiation `locked' or `blocked' inside a laser resonator on output energy and efficiency of lasing on selected wavelengths. The influence of laser mixture contents, gas pressure and temperature, laser pulse length and spectral width upon the laser characteristics also has been studied. A use of frequency selection and Q-switching decreases the laser efficiency dramatically from approximately 30% for non-selected (NS) free-running (FR) mode of operation down to approximately 0.5% ((tau) out equals 5 microsecond(s) ) for optimal wavelength ((lambda) equals 5.3 micrometers ) and to 0.1% at the long wave edge of laser spectrum ((lambda) approximately 6 micrometers ). Output energy and laser efficiency strongly depend on the number of short pulses in a train for a single electrical pumping pulse. For instance, eight short pulses lasing ((tau) out approximately 5 microsecond(s) ) has increased the output energy up to approximately 0.5 J (0.6 J/l Amagat) and efficiency up to 0.6%. For some wavelengths the output energy and laser efficiency of FS QS CO laser do not strongly depend on temperature within 100 - 150 K interval. Comparative analysis of NS FR, FS FR, NS QS and FS QS mode of operation of carbon monoxide laser has been done.