  The effect of inter-Landau-band mixing on electron localization in an integer
quantum Hall system is studied. We find that mixing of localized states with
{\it opposite chirality} tends to delocalize the states. This delocalization
effect survives the quantum treatment. Extended states form bands because of
this mixing, as we show through a numerical calculation on a two-channel
network model. Based on this result, we propose a new phase diagram with a
narrow {\it metallic} phase that separates any neighboring QH phases from each
other and also separates each of them from the insulating phase. We reanalyzed
the data from recent non-scaling experiments, and show that they are {\it
consistent} with our theory.
