  In the framework of the quasar-radio galaxies unification the radio emitting
lobes of FRII radio galaxies are pervaded by an intense quasar radiation
field.Inverse Compton (IC) scattering between the relativistic electrons and
the IR-optical photons from a hidden quasar may provide an important
contribution to the X-ray emission of these radio galaxies. The soft X-ray
emission properties of six strong, high redshift FRIIs (3C 277.2, 280, 294,
324, 356, 368) are compared with our model expectations,taking into account
also the contribution from the IC-scattering of the CMB photons with the radio
electrons. We find that the soft X-ray luminosities and spectra of five out six
sources can be satisfactorily explained by our model with the exception of 3C
324 whose X-ray emission is probably dwarfed by that of the galaxies'cluster of
which this sources is a member. One important effect is the prediction that the
observed X-ray emission associated with the two radio lobes would be asymmetric
if the radio axis is inclined with respect to the plane of the sky, the
far-away lobe being the more luminous.The ratio between the X-ray luminosities
of the two lobes is derived for several values of the inclination of the radio
axis.However, the predicted angular sizes of these distant radio galaxies are
small and difficult to be resolved with present X-ray facilities.
