  An approach, based on the use of the quasiclassical Green's function, is
developed for investigating high-energy quantum electrodynamical processes in
combined strong laser and atomic fields. Employing an operator technique, we
derive the Green's function of the Dirac equation in an arbitrary plane wave
and a localized potential. Then, we calculate the total cross section of
high-energy electron-positron photoproduction in an atomic field of arbitrary
charge number (Bethe-Heitler process) in the presence of a strong laser field.
It is shown that the laser field substantially modifies the cross section at
already available incoming photon energies and laser parameters. This makes it
feasible to observe the analogous effect in a laser field of the
Landau-Pomeranchuk-Migdal effect for the Bethe-Heitler process.
