  We consider the two-level correlation function in two-dimensional disordered
systems. In the non-ergodic diffusive regime, at energy $\epsilon>E_{c}$
($E_{c}$ is the Thouless energy), it is shown to be completely determined by
the weak localization effects, thus being extremely sensitive to time-reversal
and spin symmetry breaking: it decreases drastically in the presence of
magnetic field or magnetic impurities and changes its sign in the presence of a
spin-orbit interaction. In contrast to this, the variance of the levels number
fluctuations is shown to be almost unaffected by the weak localization effects.
