  A truncation scheme for the Dyson-Schwinger equations of QCD in Landau gauge
is presented which implements the Slavnov-Taylor identities for the 3-point
vertex functions. Neglecting contributions from 4-point correlations such as
the 4-gluon vertex function and irreducible scattering kernels, a closed system
of equations for the propagators is obtained. For the pure gauge theory without
quarks this system of equations for the propagators of gluons and ghosts is
solved in an approximation which allows for an analytic discussion of its
solutions in the infrared: The gluon propagator is shown to vanish for small
spacelike momenta whereas the ghost propagator is found to be infrared
enhanced. The running coupling of the non-perturbative subtraction scheme
approaches an infrared stable fixed point at a critical value of the coupling,
$\alpha_c \simeq 9.5$. The gluon propagator is shown to have no Lehmann
representation. The gluon and ghost propagators obtained here compare favorably
with recent lattice calculations. Results for the quark propagator in the
quenched approximation are presented.
