Abstract In this paper we consider the problem of global uniform
convergence of spectral expansions and their derivatives,
$\sum_{n=1}^{\infty}f_nu^{(j)}_n(x)$
$(j=0,1,\dots)$, generated by nonnegative selfadjoint extensions of
the operator $\Cal L(u)(x) =  u^{\prime\prime}(x) + q(x)u(x)$ with
discrete spectrum, for functions from the class
$W^{(1)}_2(G)$, where $G$ is a finite interval of the
real axis. Two theorems giving conditions on functions $q(x)$, $f(x)$
which are sufficient for the absolute and uniform convergence on $\overline
G$ of the mentioned series, are proved. Also, some convergence rate
estimates are obtained.
