  The process of photon splitting is investigated in the presence of strongly
magnetized electron-positron plasma. The amplitude of the process is calculated
in general case of plasma with nonzero chemical potential and temperature. The
polarization selection rules and corresponding partial amplitudes for allowed
splitting channels are obtained in the case of charge-symmetric plasma. It is
found that the new splitting channel forbidden in magnetized vacuum becomes
allowed. The absorption rates of the photon splitting are calculated with
taking into account of the photon dispersion and wave function renormalization.
In addition, the comparison of photon splitting and Compton scattering process
is made. The influence of the reactions under consideration on the radiation
transfer in the framework of magnetar model of SGR burst is discussed.
