  Hard diffractive photo- and electroproduction of heavy vector mesons
($J/\psi$ and $\Upsilon$) is evaluated within the leading $\alpha_s\ln{Q^2
\over\Lambda_{QCD}^2}$ approximation of QCD. In difference from our earlier
work on that subject, also the production of transversely polarized vector
mesons is calculated. Special emphasis is placed on the role of the vector
meson's $q\bar q$ light-cone wave function. In that context, conventional
non-relativistic quarkonium models and a light-front QCD bound state
calculation are critically examined and confronted with QCD expectations. Our
numerical analysis finds a significant high momentum tail in the latter wave
functions and a deviation from the expected asymptotic behavior of
$\phi_V(z,b=0)\propto z(1-z)$. We then design an interpolation to match the
quarkonium models at large inter-quark separations with QCD expectations at
small distances. We use these results to compare our predictions for the
forward differential cross section of $J/\psi$ photo- and electroproduction
with recent experimental results from HERA. In addition, our earlier discussion
of $\rho^o$ electroproduction is updated in light of recent experimental and
theoretical enhancements.
