  Maxwell-Bloch system describing the resonant propagation of electromagnetic
pulses in both two-level media with degeneracy in angle moment projection and
three-level media with equal oscillator forces is considered. The inhomogeneous
broadening of energy levels is accounted. Binary Darboux Transformation
generating the solutions of the system is constructed. Pulses corresponding to
the transition between levels with largest population difference are shown to
be stable. The solution describing the propargation of pulses in the medium
exited by the periodic wave is obtained. The hierarchy of infinitesimal
symmetries is obtained by means of Darboux transformation.
