  We show that the longitudinal polarization of the top quarks produced in the
annihilation of e+ e- or mu+ mu- into tbar t at energies near the threshold is
not affected by the large Coulomb-type corrections, which greatly modify the
total cross section. Thus the longitudinal polarization, although small, may
provide an independent information on the mass and the width of the top quark,
largely independent of the uncertainty in alpha_s.
