The dispersion relations of the collective excitations induced in a 2D spin-polarized electron gas are derived within the framework of the Landau-Silin theory applied to a two-component Fermi liquid. The quasiparticle interaction is described by spin-dependent coefficients, which are parametric functions of the initial degree of polarization. The motion of the low-energy excitations satisfies a semiclassical transport equation solved consistently with the Maxwell equations for the electromagnetic field produced by spin and charge fluctuations. The long-wavelength limit of the self-sustained oscillations is analyzed as a function of the initial degree of polarization of the system, preset by a dc magnetic induction. ͓S0163-1829͑98͒01548-3͔