  We propose a microscopic approach describing the interaction of an ideal gas
of hydrogenlike atoms with a weak electromagnetic field. This approach is based
on the Green-function formalism and an approximate formulation of the method of
second quantization for quantum many-particle systems in the presence of bound
states of particles. The dependencies of the propagation velocity and damping
rate of electromagnetic pulses on the microscopic characteristics of the system
are studied for a gas of hydrogenlike atoms. For a Bose-Einstein condensate of
alkali-metal atoms we find the conditions when the electromagnetic waves of
both the optical and microwave regions are slowed. In the framework of the
proposed approach, the influence of an external homogeneous and static magnetic
field on the slowing phenomenon is studied.
