  A new supersymmetrization of the so-called AdS-Lorentz algebra is presented.
It involves two fermionic generators and is obtained by performing an abelian
semigroup expansion of the superalgebra osp(4|1). The peculiar properties of
the aforesaid expansion method are then exploited to construct a D=4
supergravity action involving a generalized supersymmetric cosmological term in
a geometric way, only from the curvatures of the novel superalgebra. The action
obtained with this procedure is a MacDowell-Mansouri like action. Gauge
invariance and supersymmetry of the action are also analyzed.
