  The statistics of energy levels for a disordered conductor are considered in
the critical energy window near the mobility edge. It is shown that, if
critical wave functions are multifractal, the one-dimensional gas of levels on
the energy axis is ``compressible'', in the sense that the variance of the
level number in an interval is $< (\delta N)^{2} > = \chi <N>$ for $<N> >> 1$.
The compressibility, $\chi=\eta/2d$, is given ``exactly'' in terms of the
multifractal exponent $\eta=d-D_2$ at the mobility edge in a $d$-dimensional
system.
