We generalize the quasioptical description of wave beams to the case of smoothly inhomogeneous anisotropic and gyrotropic media. For brevity of the presentation, we choose a cold collisionless magnetoplasma as an example of such a medium, although the main obtained results are also valid (with some corrections) for media with spatial dispersion. For the amplitude-phase envelope of the beam, an evolution equation is derived and some of its features are analyzed.