  The static force $F_B(r)$ and the strong coupling $\alpha_F(r)$, which
defines the gluon-exchange part of $F_B(r)$, are studied in QCD background
perturbation theory (BPT). In the region $r\la 0.6 $ fm $\alpha_F(r)$ turns out
to be essentially smaller than the coupling $\alpha_B(r)$ in the static
potential. For the dimensionless function $\Phi_B(r) = r^2 F_B(r)$ the
characteristic values $\Phi_B(r_1) =1.0$ and $\Phi_B(r_0)=1.65$ are shown to be
reached at the following $Q\bar Q$ separations: $r_1\sqrt{\sigma} =0.77,
r_0\sqrt{\sigma} =1.09$ in quenched approximation and $r_1\sqrt{\sigma}=0.72,
r_0\sqrt{\sigma}=1.04$ for $n_f =3$. The numbers obtained appear to be by only
8% smaller than those calculated in lattice QCD while the values of the
couplings $\alpha_F(r_1)$ and $\alpha_F(r_0)$ in BPT are by $\sim 30% (n_f =3)$
and $50% (n_f=0)$ larger than corresponding lattice couplings. With the use of
the BPT potential good description of the bottomonium spectrum is obtained.
