  The suppression of relic gravitational waves due to their conversion into
electromagnetic radiation in a cosmological magnetic field is studied. The
coupled system of equations describing gravitational and electromagnetic wave
propagation in an arbitrary curved space-time and in external magnetic field is
derived. The subsequent elimination of photons from the beam due to their
interaction with the primary plasma is taken into account. The resulting system
of equations is solved numerically in Friedman-LeMaitre-Robertson-Walker metric
for the upper limit of the intergalactic magnetic field strength of 1 nGs. We
conclude that the gravitational wave conversion into photons in the
intergalactic magnetic field cannot significantly change the amplitude of the
relic gravitational wave and their frequency spectrum.
