On the basis of Jones' vectors and matrices formalism the equations of motion have been derived for two-frequency Fabry-Perot gas laser with a weakly anisotropic cavity when an active medium is placed in an axial magnetic field. The case of linear phase anisotropy is considered in detail. In lasers, operating at j --> j + 1 transitions in the absence of any external effects, the possibility of existence of polarization instability is shown. The influence of frequency detuning from the gain profile center on the operation of two-frequency laser has been considered. Polarization multistability has been predicted. The polarization dynamics of a laser in a longitudinal magnetic field has been investigated. The results of the theory are in agreement with the known experimental data.
