  We obtain analytically a continuum of one-dimensional ballistic extended
states in a two-dimensional disordered system, which consists of compactly
coupled random and pure square lattices. The extended states give a marginal
metallic phase with finite conductivity $\sigma_{0}=2e^2/h$ in a wide energy
range, whose boundaries define the mobility edges of a first-order
metal-insulator transition. We show current-voltage duality, $H_{\parallel}/T$
scaling of the conductivity in parallel magnetic field $H_{\parallel}$ and
non-Fermi liquid properties when long-range electron-electron interactions are
included.
