  We show that for open gauge theories, it is possible to build an off-shell
Becchi-Rouet-Stora-Tyutin (BRST) algebra together with an invariant extension
of the classical action. This is based on the introduction of auxiliary fields,
after having defined an on-shell invariant quantum action, where the
gauge-fixing action is written as in Yang-Mills type theories up to a modified
BRST operator. An application to simple supergravity is performed.
