  In this paper, admitting a de Sitter (dS)-invariant vacuum in an indefinite
inner product space, we present a Gupta-Bleuler type setting for causal and
full dS-covariant quantization of free "massless" spin-2 field in dS spacetime.
The term "massless" stands for the fact that the field displays gauge and
conformal invariance properties. In this construction, the field is defined
rigorously as an operator-valued distribution. It is covariant in the usual
strong sense: $\underline{U}_g \underline{{\cal{K}}} (X) \underline{U}_g^{-1} =
\underline{{\cal{K}}} (g.X)$, for any $g$ in the dS group, where
$\underline{U}$ is associated with the indecomposable representations of the dS
group, $SO_0(1,4)$, on the space of states. The theory, therefore, does not
suffer from infrared divergences. Despite the appearance of negative norm
states in the theory, the energy operator is positive in all physical states
and vanishes in the vacuum.
