  We present a new development in our approach to the covariant quantization of
superstrings in 10 dimensions which is based on a gauged WZNW model. To
incorporate worldsheet diffeomorphisms we need the quartet of ghosts
$(b_{zz},c^{z}, \b_{zz}, \g^{z})$ for topological gravity. The currents of this
combined system form an N=2 superconformal algebra. The model has vanishing
central charge and contains two anticommuting BRST charges, $Q_{S}=Q_{W} +
\oint \g^{z} b_{zz} + \oint \eta_{z}$ and $Q_{V} = \oint c^{z} \Big(T^{W}_{zz}
+ {1\over 2} T^{top}_{zz}\Big) + \g^{z} (B^{W}_{zz} + {1\over 2} B^{top}_{zz}
\Big)$, where $\eta_{z}$ is obtained by the usual fermionization of $\b_{zz},
\g^{z}$. Physical states form the cohomology of $Q_{S}+Q_{V}$, have nonnegative
grading, and are annihilated by $b_{0}$ and $\beta_{0}$. We no longer introduce
any ghosts by hand, and the formalism is completely Lorentz covariant.
