  Anticipating future long-baseline neutrino experiments to search for neutrino
oscillations in various oscillation channels, we have analyzed the atmospheric
neutrino data in the framework of a model with mixing of three massive neutrino
fields that can accommodate the data of solar neutrino experiments. The
oscillations of atmospheric and terrestrial neutrinos are described in this
model by three parameters: $ \Delta m^2 $ and the squared moduli of two
elements of the mixing matrix, $ | U_{e3} |^2 $ and $ | U_{\mu3} |^2 $, which
determine the amplitudes of oscillations among all active neutrinos. The
results of the analysis of the atmospheric neutrino data are presented in the
form of allowed regions in the plane of the two parameters oscillation
amplitude and $ \Delta m^2 $ for all oscillation channels to be investigated in
the future long-baseline oscillation experiments.
