The polarization dependent momentum distributions
of top quarks and their decay products are calculated
for $t\bar t$ production at future $e^+e^-$ colliders
with polarized beams. The Green function formalism
is applied to this reaction near energy threshold.
The Lippmann–Schwinger equations for the $S$-wave and
$P$-wave Green functions are solved numerically for the
QCD chromostatic potential given by the two-loop formula
at large momentum transfers and Richardson ansatz
at intermediate and small ones.
It is demonstrated that for the longitudinally polarized
electron beam an optimally polarized sample of top quarks can
be produced.
