  Theory of quantum corrections to conductivity of granular metal films is
developed for the realistic case of large randomly distributed tunnel
conductances. Quantum fluctuations of intergrain voltages (at energies E much
below bare charging energy scale E_C) suppress the mean conductance \bar{g}(E)
much stronger than its standard deviation \sigma(E). At sufficiently low
energies E_* any distribution becomes broad, with \sigma(E_*) ~ \bar{g}(E_*),
leading to strong local fluctuations of the tunneling density of states.
Percolative nature of metal-insulator transition is established by combination
of analytic and numerical analysis of the matrix renormalization group
equations.
