  A general analysis of polarization phenomena for coherent meson
electroproduction on deuterons, $e+ d\to e+ d +P^0$, where $P^0$ is a
pseudoscalar $\pi ^0$ or $\eta$-meson, is presented. The spin structure of the
electromagnetic current for $P^0$-production at threshold is parametrized in
terms of specific (inelastic) threshold electromagnetic form factors which
depend on the momentum transfer squared and the effective mass of the produced
hadronic system. We give expressions for the structure functions of the
reaction $e+\vec{d}\to e +d+ P^0$ (where the deuteron target is polarized) in
terms of these threshold form factors. The spin and isospin structures of the
$\gamma ^{*}+d\to d+P^0$ amplitudes (where $\gamma ^*$ is a virtual photon) is
established in the framework of the impulse approximation and relationships
between meson electroproduction on deuterons and on nucleons are given. The
reaction of $\pi^0$ electroproduction on deuterons is investigated in detail
both at threshold and in the region of $\Delta $-isobar excitation, using the
effective Lagrangian approach for the calculation of the amplitudes of the
elementary process $\gamma^*+N\to N+\pi$. Special attention is devoted to the
analysis of all standard contributions to the exclusive cross section for
$d(e,e\pi^0)d$, which are functions of the momentum transfer square, $k^2$, of
the excitation energy of the produced hadrons and of the pion production angle,
in a region of relatively large momentum transfer. The sensitivity of these
contributions to different parametrizations of the $\gamma^*\pi\omega$ form
factor as well as to the choice of $NN-$potential is discussed.
