  We study the sensitivity to the Z' couplings of the processes $e^+e^-\to
l^+l^-,\bar{b}b$ and $\bar{c}c$ at the linear collider with $\sqrt{s}=500 GeV$
with initial beam polarization, for typical extended model examples. To this
aim, we use suitable integrated, polarized, observables directly related to the
helicity cross sections that carry information on the individual Z' chiral
couplings to fermions. We discuss the derivation of separate, model-independent
limits on the couplings in the case of no observed indirect Z' signal within
the expected experimental accuracy. In the hypothesis that such signals were,
indeed, observed we assess the expected accuracy on the numerical determination
of such couplings and the consequent range of Z' masses where the individual
models can be distinguished from each other as the source of the effect.
