  We calculate the 3-loop bare $\beta$-function of QCD, formulated on the
lattice with the clover fermionic action. The dependence of our result on the
number of colors $N$, the number of fermionic flavors $N_f$, and the clover
parameter $c_{SW}$, is shown explicitly. A direct outcome of our calculation is
the two-loop relation between the bare coupling constant $g_0$ and the one
renormalized in the MS-bar scheme. Further, we can immediately derive the
three-loop correction to the relation between the lattice $\Lambda$-parameter
and $g_0$, which turns out to be very pronounced.
  We also calculate the critical value of the hopping parameter, $\kappa_c$, in
the clover action, to two loops in perturbation theory. This quantity is an
additive renormalization; as such, it exhibits a linear divergence in the
lattice spacing. We compare our results to non perturbative evaluations of
$\kappa_c$ coming from MC simulations.
