Chiral behaviour of the lattice B$_{K}$-parameter with the Wilson and Clover actions at $\beta$ = 6.0

We present results for the kaon B-parameter B_K from a sample of 200 configurations using the Wilson action and 460 configurations using the SW-Clover action, on a 18^3 \times 64 lattice at \beta=6.0. We compare results obtained by renormalizing the relevant operator with different ``boosted" values of the strong coupling constant \alpha_s. In the case of the SW-Clover action, we also use the operator renormalized non-perturbatively. In the Wilson case, we observe a strong dependence of B_K on the prescription adopted for \alpha_s, contrary to the results of the Clover case which are almost unaffected by the choice of the coupling. We also find that the matrix element of the operator renormalized non-perturbatively has a better chiral behaviour. This gives us our best estimate of the renormalization group invariant B-parameter, \hat B_K=0.86 \pm 0.15.