The conservation laws and the densities of electromagnetic field energy and momentum in dispersive media

New general nonstationary balance equations for energy and momentum densities of field-matter system based on rigorous nonstationary approach for their definitions with dependence from the field creation prehistory have been obtained. Also the transport velocities of these densities have been derived. The concrete examination and detailed consideration have been performed for simplest dispersion law which is defined by the conductivity connected with the dissipation. For this case the energy and momentum densities, phase velocity, group velocity, and transport velocities of energy and momentum have been determined. The energy and momentum conservation have been shown for plane electromagnetic wave in the conducting medium and for plane wave diffraction on the conducting plate.