  A theory of mesoscopic fluctuations in disordered thin superconducting films
in a parallel magnetic field is developed. At zero temperature, the
superconducting state undergoes a phase transition into a state characterized
by superfluid densities of random signs, instead of a spin polarized disordered
Fermi liquid phase. Consequently, the ground state belongs to the same
universality class as the 2D XY spin glass. As the magnetic field increases
further, mesoscopic pairing states are nucleated in an otherwise homogeneous
spin polarized disordered Fermi liquid. The statistics of these pairing states
is universal depending on the sheet conductance of the 2D film.
