  We prove, in standard notation from spectral theory, the asymptotic formula
($B>0$) $$ \sum_{\kappa_j\le T}\alpha_j H_j(1/2) = ({T\over\pi})^2 - BT\log T +
O(T(\log T)^{1/2}), $$ by using an approximate functional equation for
$H_j(1/2)$ and the Bruggeman--Kuznetsov trace formula. We indicate how the
error term may be improved to $O(T(\log T)^\epsilon)$.
