Within the framework of the method of orbits, expressions have been obtained for the vacuum averages of the energy-momentum tensor of a scalar field with an arbitrary coupling constant in a spacetime with a nonstationary metric of Robertson–Walker type, where space is a homogeneous Riemannian manifold. It is shown that the vacuum averages of the energy-momentum tensor are determined by the complete set of solutions of the reduced equation with a smaller number of independent variables and with algebraic characteristics of homogeneous space.