  The 2003 October 28 (X17.2) eruptive flare was a unique event. The coronal
electric field and the {\pi}-decay {\gamma}-ray emission flux had the highest
values ever inferred in solar flares. This study reveals physical links between
the magnetic reconnection process, the energy release, and the acceleration of
electrons and ions to high energies in the chain of the magnetic energy
transformations in the impulsive phase of the solar flare. The global
reconnection rate and the local reconnection rate are calculated from flare
ribbon separation in H{\alpha} filtergrams and photospheric magnetic field
maps. Available results of INTEGRAL and CORONAS-F/SONG observations are
combined with Konus-Wind data to quantify time behavior of electron and proton
acceleration. Prompt {\gamma}-ray lines and delayed 2.2 MeV line temporal
profiles observed with Konus-Wind and INTEGRAL/SPI used to detect and quantify
the nuclei with energies of 10-70 MeV. The global and local reconnection rates
reach their peaks at the end of the main rise phase of the flare. The spectral
analysis of the high-energy {\gamma}-ray emission revealed a close association
between the acceleration process efficiency and the reconnection rates.
High-energy bremsstrahlung continuum and narrow {\gamma}-ray lines were
observed in the main rise phase. In the main energy release phase, the upper
energy of the bremsstrahlung spectrum was significantly reduced and the
pion-decay {\gamma}-ray emission appeared abruptly. We discuss the reasons why
the change of the acceleration regime occurred along with the large-scale
magnetic field restructuration of this flare. We argue that the main energy
release and proton acceleration up to subrelativistic energies began just when
the reconnection rate was going through the maximum, i.e., after a major change
of the flare topology.
