  Using a modification of the Shapiro approach, we introduce the two-parameter
family of conductance distributions W(g), defined by simple differential
equations, which are in the one-to-one correspondence with conductance
distributions for quasi-one-dimensional systems of size L^{d-1}\times L_z,
characterizing by parameters L/\xi and L_z/L (\xi is the correlation length, d
is the dimension of space). This family contains the Gaussian and log-normal
distributions, typical for the metallic and localized phases. For a certain
choice of parameters, we reproduce the results for the cumulants of conductance
in the space dimension d=2+\epsilon obtained in the framework of the
\sigma-model approach. The universal property of distributions is existence of
two asymptotic regimes, log-normal for small g and exponential for large g. In
the metallic phase they refer to remote tails, in the critical region they
determine practically all distribution, in the localized phase the former
asymptotics forces out the latter. A singularity at g=1, discovered in
numerical experiments, is admissible in the framework of their calculational
scheme, but related with a deficient definition of conductance. Apart of this
singularity, the critical distribution for d=3 is well described by the present
theory. One-parameter scaling for the whole distribution takes place under
condition, that two independent parameters characterizing this distribution are
functions of the ratio L/\xi.
