  We report on the detection of a soft spatially-extended component of X-ray
emission around four intermediate-redshift 3C quasars observed with Chandra:
3C254, 3C263, 3C275.1 and 3C281. The bolometric luminosity of this emission
ranges over 0.3-1.6 times 10^{44}erg/s, and extends to lengthscales of over 350
kpc at the redshift of the quasar. The X-rays are most likely thermal emission
from the intracluster medium of a cluster of galaxies around each quasar, which
provides the working surface for the powerful radio lobes. Some X-ray emission
is also seen to be associated with the radio plasma.
