  The dependence of the differential cross section and polarization observables
in the $\bar N+N\to \pi +e^++e^-$ reaction on the polarizations of the proton
target and antiproton beam (the produced electron may be unpolarized or
longitudinally polarized) have been derived in a general form using hadron
electromagnetic current conservation and $P-$ invariance of the hadron
electromagnetic interaction. The analysis was done for the case of an exclusive
experimental setup where the produced electron and pion are detected in
coincidence. The explicit dependence of all polarization observables on two,
from five, kinematic variables (the azimuthal angle $\varphi$ and the
virtual-photon parameter $\epsilon$), have been obtained assuming
one-photon-exchange. The application to the particular case of a mechanism
which contains information on time-like proton form factors in the unphysical
region is considered in the Born approximation.
