  An essential role in the asteroidal dynamics is played by the mean motion
resonances. Two-body planet-asteroid resonances are widely known, due to the
Kirkwood gaps. Besides, so-called three-body mean motion resonances exist, in
which an asteroid and two planets participate. Identification of asteroids in
three-body (namely, Jupiter-Saturn-asteroid) resonances was initially
accomplished by D.Nesvorny and A.Morbidelli (1998), who, by means of visual
analysis of the time behaviour of resonant arguments, found 255 asteroids to
reside in such resonances. We develop specialized algorithms and software for
massive automatic identification of asteroids in the three-body, as well as
two-body, resonances of arbitrary order, by means of automatic analysis of the
time behaviour of resonant arguments. In the computation of orbits, all
essential perturbations are taken into account. We integrate the asteroidal
orbits on the time interval of 100000 yr and identify main-belt asteroids in
the three-body Jupiter-Saturn-asteroid resonances up to the 6th order
inclusive, and in the two-body Jupiter-asteroid resonances up to the 9th order
inclusive, in the set of ~250000 objects from the "Asteroids - Dynamic Site"
(AstDyS) database. The percentages of resonant objects, including
extrapolations for higher-order resonances, are determined. In particular, the
observed fraction of pure-resonant asteroids (those exhibiting resonant
libration on the whole interval of integration) in the three-body resonances up
to the 6th order inclusive is approximately 0.9% of the whole set; and, using a
higher-order extrapolation, the actual total fraction of pure-resonant
asteroids in the three-body resonances of all orders is estimated as
approximately 1.1% of the whole set.
