Rytov's method is generalized for the case when the regularly inhomogeneous ionosphere contains local irregularities of deterministical and statistical nature. An integral representation of the point source field is constructed which takes into account the multibeam effects including strong interference of the beams field, i.e., caustics and foci formation and so on. By means of the representation developed, some problems of HF wave propagation are solved. Among these is the diffraction of a point source field on an ambipolar diffusing local inhomogeneity of the ionosphere. The calculations of the power spectra of the fluctuations of the phase and amplitude of a single-hop path field due to ionospherical electron density irregularities are also presented. The calculations are compared with the results of experimental investigations.