  We consider a $D$-dimensional gravitational model with a Gauss-Bonnet term
and the cosmological term $\Lambda$. We restrict the metrics to diagonal
cosmological ones and find for certain $\Lambda$ a class of solutions with
exponential time dependence of three scale factors, governed by three
non-coinciding Hubble-like parameters $H >0$, $h_1$ and $h_2$, corresponding to
factor spaces of dimensions $m > 2$, $k_1 > 1$ and $k_2 > 1$, respectively,
with $k_1 \neq k_2$ and $D = 1 + m + k_1 + k_2$. Any of these solutions
describes an exponential expansion of $3d$ subspace with Hubble parameter $H$
and zero variation of the effective gravitational constant $G$. We prove the
stability of these solutions in a class of cosmological solutions with diagonal
metrics.
