  We propose a modification of the Sp(2) covariant superfield quantization to
realize a superalgebra of generating operators isomorphic to the massless limit
of the corresponding superalgebra of the osp(1,2) covariant formalism. The
modified scheme ensures the compatibility of the superalgebra of generating
operators with extended BRST symmetry without imposing restrictions eliminating
superfield components from the quantum action. The formalism coincides with the
Sp(2) covariant superfield scheme and with the massless limit of the osp(1,2)
covariant quantization in particular cases of gauge-fixing and solutions of the
quantum master equations.
