  A linear but global numerical model for the magnetorotational instability
(MRI) in disk geometry is considered to estimate the instability parameters for
galaxies. Similarity rules suggested by a local analysis are applied to reveal
a universal behavior approached by the results of global calculations for large
magnetic Prandtl numbers. The findings are used to estimate the MRI
characteristics for galaxies with their very large magnetic Prandtl numbers
which cannot be attained in any numerical simulations. The resulting minimum
field for the instability, Bmin 10-25 G, is small compared to any seed fields
currently discussed. The growth times of MRI are estimated to be on the order
of the rotation period of the inner rigidly-rotating core, i.e. ~100 Myr.
Global MRI excites preferentially the magnetic field modes of quadrupolar
symmetry.
