  Particle acceleration in clusters of galaxies is expected to take place at
both merger and accretion shocks. The electron component may be energized to
energies of several TeV, and upscatter a small fraction of the photons in the
cosmic microwave background up to gamma ray energies. We address here the issue
of the detectability of the gamma radiation generated either in merger events
or during the accretion of matter onto cluster potential wells. The predictions
are specialized to the cases of GLAST and AGILE, for which a few tens of
clusters are expected to be detected, and to Cherenkov telescopes, for which
however the perspectives do not appear to be optimistic.
