This part of the paper deals with a variational approach. The general scheme is given and two examples are presented: free oscillations of an electromagnetic field in a cavity filled with an inhomogeneous dispersive resonant medium and wave propagation in a longitudinally homogeneous plasma cylinder in an infinitely strong magnetic field. A comparison shows good agreement of results of a variational approach with results of an exact numerical solution. Possible ways of improving accuracy are discussed. ©1996 American Institute of Physics.