  We study the neutrino mass generation in the $SU(4)_L \otimes U(1)_X$
electroweak extension of the standard model by considering non-renormalizable
dimension five effective operators. It is shown that there exist two topologies
for the realizations of such an operator at the tree-level and for one of the
three-family models is explore the neutrino phenomenology after extending its
particle content with an $SU(4)_L$ fermion singlet and a scalar decuplet.
Constraints in the available parameters space of the model are partially
discussed.
