  Transport in a two-dimensional electron gas subject to an external magnetic
field is analyzed in the presence of a \textit{longitudinal barrier.} We show
that \textit{quantum interference of the edge states} bound by the longitudinal
barrier results in a drastic change of the electron motion: the degenerate
discrete Landau levels are transformed into an alternating sequence of energy
bands and energy gaps. These features of the electron spectrum should result in
a high sensitivity of thermodynamic and transport properties of the 2D electron
gas to external fields. In particular, we predict giant oscillations of the
ballistic conductance and discuss nonlinear current-voltage characteristics,
coherent Bloch oscillations and effects of impurities
