  A field-theoretic description of the critical behaviour of systems with
quenched defects obeying a power law correlations $\sim |{\bf x}|^{-a}$ for
large separations ${\bf x}$ is given. Directly for three-dimensional systems
and different values of correlation parameter $2\leq a \leq 3$ a
renormalization analysis of scaling function in the two-loop approximation is
carried out, and the fixed points corresponding to stability of the various
types of critical behaviour are identified. The obtained results essentially
differ from results evaluated by double $\epsilon, \delta$ - expansion. The
critical exponents in the two-loop approximation are calculated with the use of
the Pade-Borel summation technique.
