  The conventional theory of superconducting alloys does not take into account
a discreet character of impurities. Experimental data for superfluid $^3$He in
aerogel and for some of high-$T_c$ superconductors reveal a significant
discrepancy between the observed temperatures $T_c$ of their transitions in the
superfluid or superconducting state and that predicted by the theory. Here a
theoretical scheme is presented for finding corrections to the $T_c$
originating from spatial correlations between impurities. Analysis is limited
to the Ginzburg and Landau temperature region. The shift of $T_c$ with respect
to the pure material is represented as a series in concentration of the
impurities $x$. In the first order on $x$ the conventional mean-field result
for the lowering of $T_c$ is recovered. Contribution of correlations enters the
second order term. It is expressed via the structure factor of the ensemble of
impurities. For superfluid $^3$He in silica aerogel the sign of the correction
corresponds to an enhancement of the $T_c$ so that the resulting pairbreaking
effect of impurities is weakened. When correlation radius of impurities $R$
exceeds the coherence length of the superfluid $\xi_0$ the contribution of
correlations to the shift of $T_c$ acquires a factor $\sim(R/\xi_0)^2$ and the
weakening of the pairbreaking effect becomes appreciable. The presented scheme
is applied to the superfluid $^3$He in aerogel.
