  In this paper, first we give a notion for linear Weingarten spacelike
hypersurfaces with $P+aH=b$ in a locally symmetric Lorentz space $L_{1}^{n+1}$.
Furthermore, we study complete or compact linear Weingarten spacelike
hypersurfaces in locally symmetric Lorentz spaces $L_{1}^{n+1}$ satisfying some
curvature conditions. By modifying Cheng-Yau's operator $\square$ given in
{\cite{ChengYau77}}, we introduce a modified operator $L$ and give new
estimates of $L(nH)$ and $\square(nH)$ of such spacelike hypersurfaces.
Finally, we give partial generalizations of some conjectures in locally
symmetric Lorentz spaces $L_{1}^{n+1}$.
