  In this paper we propose four different methods to determine Sturm-Liouville
operator on an interval $(a,b)$ in case, when a potential $q(x)$ is a
distribution from the Sobolev space with negative index of smoothness, i.e.
(q\in W_2^{-\theta}), where (\theta\le 1). The main and second terms of
asymptotic series for eigenvalues and eigenfunctions of these operators are
obtained and the remaining terms are estimated depending on the class of
smoothness of potential /(q/). Particular families of potentials, not belonging
to the space (W_2^{-1}) are studied as well.
