  We propose a model which represents a four-dimensional version of Ponzano and
Regge's three-dimensional euclidean quantum gravity. In particular we show that
the exponential of the euclidean Einstein-Regge action for a $4d$-discretized
block is given, in the semiclassical limit, by a gaussian integral of a
suitable $12j$-symbol. Possible developments of this result are discussed.
