  In this work, firstly in the Hilbert space of vector-functions L^2
(H,(-\infty,a)\bup(b,+\infty)),a<b all selfadjoint extensions of the minimal
operator generated by linear singular symmetric differential expression
l(\cdot)=i d/dt+A with a selfadjoint operator coefficient A in any Hilbert
space H, are described in terms of boundary values. Later structure of the
spectrum of these extensions is investigated.
