  The proton ordering model for the KH$_{2}$PO$_{4}$ type ferroelectrics is
modified by taking into account the dependence of the effective dipole moments
on the proton ordering parameter. Within the four-particle cluster
approximation we calculate the crystal polarization and explore the
electrocaloric effect. Smearing of the ferroelectric phase transition by a
longitudinal electric field is described. A good agreement with experiment is
obtained.
