  We elucidate the geometry of the polynomial formulation of the non-abelian
Stueckelberg mechanism. We show that a natural off-shell nilpotent BRST
differential exists allowing to implement the constraint on the sigma field by
means of BRST techniques. This is achieved by extending the ghost sector by an
additional U(1) factor (abelian embedding). An important consequence is that a
further BRST-invariant but not gauge-invariant mass term can be written for the
non-abelian gauge fields. As all versions of the Stueckelberg theory, also the
abelian embedding formulation yields a non power-counting renormalizable theory
in D=4. We then derive its natural power-counting renormalizable extension and
show that the physical spectrum contains a physical massive scalar particle.
Physical unitarity is also established. This model implements the spontaneous
symmetry breaking in the abelian embedding formalism.
