  We consider the procedure for calculating the pair correlation function in
the context of the Cluster Variation Methods. As specific cases, we study the
pair correlation function in the paramagnetic phase of the Ising model with
nearest neighbors, next to the nearest neighbors and plaquette interactions in
two and three dimensions. In presence of competing interactions, the so called
disorder line separates in the paramagnetic phase a region where the
correlation function has the usual exponential behavior from a region where the
correlation has an oscillating exponentially damped behavior. In two
dimensions, using the plaquette as the maximal cluster of the CVM
approximation, we calculate the phase diagram and the disorder line for a case
where a comparison is possible with results known in literature for the
eight-vertex model. In three dimensions, in the CVM cube approximation, we
calculate the phase diagram and the disorder line in some cases of particular
interest. The relevance of our results for experimental systems like mixtures
of oil, water and surfactant is also discussed.
