  We propose a parameterization for contributions of an infinite set of
diagrams (bubble chains) into physical observables represented as integrals of
running coupling constant over the finite region in momentum space. The
perturbation theory part of contributions is rendered well-defined by the
principal value prescrition for treating the Landau pole while the rest is
connected to the gluon condensate in case of observables allowing the OPE
analysis. The hypothesis of universality, i.e. the use of our parameterization
for non-OPE cases, is discussed.
