  Original Whitham's method of derivation of modulation equations is applied to
systems whose dynamics is described by a perturbed Korteweg-de Vries equation.
Two situations are distinguished: (i) the perturbation leads to appearance of
right-hand sides in the modulation equations so that they become non-uniform;
(ii) the perturbation leads to modification of the matrix of Whitham
velocities. General form of Whitham modulation equations is obtained for each
case. The essential difference between them is illustrated by an example of
so-called `generalized Korteweg-de Vries equation'. Method of finding
steady-state solutions of perturbed Whitham equations in the case of
dissipative perturbations is considered.
