BRST invariance and Poincaré-Cartan forms

BRST quantization of gauge theories is considered on the basis of Poincaré-Cartan forms in the framework of global variational calculus on fibred manifolds. It is pointed out that the BRST transformation admits a jet-prolonged formulation which is in fact a ≪generalized symmetry≫ of the BRST-invariant Lagrangian (a well-known concept in the framework of integrable systems). We show that the Poincaré-Cartan forms are invariant under this extended BRST transformation only modulo contact terms, which vanish on all sections anda fortiori on solutions of field equations.