  A four-fermion model with additional higher-derivative terms is investigated
in an external electromagnetic field. The effective potential in the leading
order of large-N expansion is calculated in external constant magnetic and
electric fields.
  It is shown that, in contrast to the former results concerning the universal
character of "magnetic catalysis" in dynamical symmetry breaking, in the
present higher-derivative model the magnetic field restores chiral symmetry
broken initially on the tree level. Numerical results describing a second-order
phase transition that accompanies the symmetry restoration at the quantum level
are presented.
