  In the open problem of classification of rational cuspidal plane curves it is
essential to find good necessary conditions on the type of singularities of a
curve C in order C to exit. Motivated by the study of the Seiberg-Witten
invariant of normal surface singularities whose link is a rational homology
sphere we have found good candidates for such necessary conditions. In this
paper we study this compatibility conditions and proved them for all curves
whose logarithmic Kodaira dimension is strictly less than 2.
