  We present a detailed study of the morphological features of 22 rich galaxy
clusters. Our sample is constructed from a cross-correlation of optical
(Abell+APM) data with X-ray (0.1 - 2.4) keV ROSAT pointed observations. We
systematically compare cluster images and morphological parameters in an
attempt to reliably identify possible substructure in both optical and the
X-ray images. To this end, we compute various moments of the optical and X-ray
surface-brightness distribution such as the ellipticities, center-of-mass
shifts and ellipsoidal orientations. We assess the significance of our results
using Monte Carlo simulations. We find significant correlations between the
optical and X-ray morphological parameters, indicating that in both parts of
the spectrum it is possible to identify correctly the dynamical state of a
cluster. Most of our clusters (17/22) have a good 1-to-1 correspondence between
the optical and the X-ray images and about 10 appear to have strong indications
of substructure. This corresponds to a minimum percentage of order 45 per cent
which is in very good accordance with other similar analyses. Finally, 5 out of
22 systems seem to have distinct subclumps in the optical which are not
verified in the X-ray images, and thus are suspect of being due to optical
projection effects. These results will serve as a useful guide in interpreting
subsequent analyses of large optical cluster catalogues.
