  We examine the effect of disorder on the electromagnetic response of quantum
Hall stripes using an effective elastic theory to describe their low-energy
dynamics, and replicas and the Gaussian variational method to handle disorder
effects. Within our model we demonstrate the existence of a depinning
transition at a critical partial Landau level filling factor $\Delta\nu_c$. For
$\Delta\nu<\Delta\nu_c$, the pinned state is realized in a replica symmetry
breaking (RSB) solution, and the frequency-dependent conductivities in both
perpendicular and parallel to the stripes show resonant peaks. These peaks
shift to zero frequency as $\Delta\nu\to \Delta\nu_c$. For
$\Delta\nu\ge\Delta\nu_c$, we find a {\em partial RSB (PRSB)} solution in which
there is free sliding only along the stripe direction. The transition is
analogous to the Kosterlitz-Thouless phase transition.
