  The processes of neutrino production of electron-positron pairs, $\nu \bar\nu
\to e^- e^+$ and $\nu \to \nu e^- e^+$, in a magnetic field of arbitrary
strength, where electrons and positrons can be created in the states
corresponding to excited Landau levels, are analysed. The results can be
applied for calculating the efficiency of the electron-positron plasma
production by neutrinos in the conditions of the Kerr black hole accretion disc
considered by experts as the most possible source of a short cosmological gamma
burst.
