  We investigate small$-x$ resummation effects in QCD coefficient functions for
$Z_0g$ and $Wg$ fusion processes, and we compare them with the known ones of
$\gamma g$ type. We find a strong process dependence, that we argue to be due
to the possible presence of collinear singularities for either small or large
$\k$ of the exchanged gluon. For top quark production, we find that the $gg\ra
t\bar{t}$ and $Z_0g\ra t\bar{t}$ channels have larger resummation enhancements
than the $Wg\ra t\bar{t}$ one.
