  The level curvature distribution function is studied beyond the random matrix
theory for the case of T-breaking perturbations over the orthogonal ensemble.
The leading correction to the shape of the level curvature distribution is
calculated using the nonlinear sigma-model. The sign of the correction depends
on the presence or absence of the global gauge invariance and is different for
perturbations caused by the constant vector-potential and by the random
magnetic field. Scaling arguments are discussed that indicate on the
qualitative difference in the level statistics in the dirty metal phase for
space dimensionalities $d<4$ and $d>4$.
