<1> A weakly nonlinear process of propagation of an electromagnetic pulse with a linear modulation of the carrier frequency in a waveguide structure characterized by different scales of inhomogeneity in the transverse and longitudinal directions is considered. Waveguide channels with such properties are formed, in particular, in the ionospheric F layer due to its stratification under the action of powerful modifying pulses. Thus the method proposed is applicable to a description of the processes of radio wave propagation in the ionosphere with local irregularities. The method also may be used for controlling the parameters (duration, amplitude, etc.) of powerful chirped pulses. Chirps are classified in accordance with the ratio between pulse duration and modulation depth. It is shown that the pulse evolution is determined by three timescales, and analytical relations for chirp parameters are established depending on the transverse and longitudinal inhomogeneity.