  It is shown that an alternative supersymmetric version of the Liouville
equation extracted from D=3 Green-Schwarz superstring equations naturally
arises as a super-Toda model obtained from a properly constrained
supersymmetric WZNW theory based on the $sl(2, R)$ algebra. Hamiltonian
reduction is performed by imposing a nonlinear superfield constraint which
turns out to be a mixture of a first- and second-class constraint on
supercurrent components. Supersymmetry of the model is realized nonlinearly and
is spontaneously broken. The set of independent current fields which survive
the Hamiltonian reduction contains (in the holomorphic sector) one bosonic
current of spin 2 (the stress--tensor of the spin 0 Liouville mode) and two
fermionic fields of spin ${3/2}$ and $-1/2$. The $n=1$ superconformal system
thus obtained is of the same kind as one describing noncritical fermionic
strings in a universal string theory. The generalization of this procedure
allows one to produce from any bosonic Lie algebra super--Toda models and
associated super-W algebras together with their nonstandard realizations.
