  In order to study the status and the possible evolution of clusters of
galaxies at intermediate redshifts (z ~ 0.1 - 0.3), as well as their spatial
correlation and relationship with the local environment, we built a sample of
candidate groups and clusters of galaxies using radiogalaxies as tracers of
dense environments. This technique - complementary to purely optical or X-ray
cluster selection methods - represents an interesting tool for the selection of
clusters in a wide range of richness, so to make it possible to study the
global properties of groups and clusters of galaxies, such as their
morphological content, dynamical status and number density, as well as the
effect of the environment on the radio emission phenomena. In this paper we
describe the compilation of a catalogue of 16000 radio sources in the region of
the South Galactic Pole extracted from the publicly available NRAO VLA Sky
Survey maps, and the optical identification procedure with galaxies brighter
than b_J=20.0 in the EDSGC Catalogue. The radiogalaxy sample, valuable for the
study of radio source populations down to low flux levels, consists of 1288
identifications and has been used to detect candidate groups and clusters
associated to NVSS radio sources. In a companion paper we will discuss the
cluster detection method, the cluster sample as well as first spectroscopic
results.
