  In the framework of analytic approach to QCD, which has been recently
intensively developed, the dependence of nonperturbative contributions in a
running coupling of strong interaction on initial perturbative approximation to
3-loop order is studied. The nonperturbative contributions are obtained in an
explicit form. In the ultraviolet region they are shown to be represented in
the form of the expansion in the inverse powers of Euclidean momentum squared.
The expansion coefficients are calculated for different numbers of active quark
flavors $n_f$ and for different numbers of loops taken into account. For all
$n_f$ of interest it is shown that 2-loop order and 3-loop order corrections
result in partial compensation of 1-loop order leading in the ultraviolet
region nonperturbative contribution.
