A perturbation scheme based on the slow adiabatic variation of the radiation-field characteristics is applied to the Maxwell-Bloch equations. The two leading orders in the perturbation expansion yield a set of partial differential equations for $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}},t)$, $\ensuremath{\omega}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}},t)$, and $a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}},t)$ (the local wave vector and frequency and the field amplitude). All the coefficients of these equations are derivable from a single dispersion function $H(\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}},\ensuremath{\omega},a)$, this feature is used to further reduce the equations to a set of Hamilton-Jacobi-type ordinary differential equations (ray equations). Unlike the linear geometric optics case the properties of the "local lens" seen by a ray depend also on the amplitude of the field propagating along neighboring rays. A method to derive additional equations for the evolution of the local lens along a single ray and to decouple the equations for different rays is described, the resultant enlarged set of ray equations is derived. The limitations and advantages of this approximation scheme are discussed in comparison with other approaches.