Constrained current algebras and $g/u(1)^d$ conformal field theories

Operator quantization of the WZNW theory invariant with respect to an affine Kac-Moody algebra $\hat g$ with constrained $\hat {u}(1)^d$ currents is performed using Dirac's procedure. Upon quantization the initial energy-momentum tensor is replaced by the $g/u(1)^d$ coset construction. The $\hat {su}(2)$ WZNW theory with a constrained $\hat u(1)$ current is equivalent to the $su(2)/u(1)$ conformal field theory.