  The abstract interpolation problem (AIP) in the Schur class was posed V.
Katznelson, A. Kheifets and P. Yuditskii in 1987 as an extension of the V.P.
Potapov's approach to interpolation problems. In the present paper an analog of
the AIP for Nevanlinna classes is considered. The description of solutions of
the AIP is reduced to the description of L-resolvents of some model symmetric
operator associated with the AIP. The latter description is obtained by using
the M.G. Krein's theory of L-resolvent matrices. Both regular and singular
cases of the AIP are treated. The results are illustrated by the following
examples: bitangential interpolation problem, full and truncated moment
problems. It is shown that each of these problems can be included into the
general scheme of the AIP.
