  We describe a canonical covariant formulation of the Green-Schwarz
Superstring which allows the construction of a new covariant action canonically
equivalent to the Green-Schwarz action but subjected only to first class
constraints. From this action the correct BRST operator for the quantization of
the Green-Schwarz Superstring may be constructed. Also the gauge fixed action
in the Light-Cone gauge may be reobtained. The action presented in this letter
generalizes in a non-trivial form the action introduced by Kallosh for the
Brink-Schwarz-Casalbuoni Superparticle.
