LSI +61 ^ { \circ } 303 is one of the few X-ray binaries with Be star companion from which both radio and high-energy gamma-ray emission have been observed .
We present XMM-Newton and INTEGRAL observations which reveal variability of the X-ray spectral index of the system .
The X-ray spectrum is hard ( photon index \Gamma \simeq 1.5 ) during the orbital phases of both high and low X-ray flux .
However , the spectrum softens at the moment of transition from high to low X-ray state .
The spectrum of the system in the hard X-ray band does not reveal the presence of a cut-off ( or , at least a spectral break ) at 10-60 keV energies , expected if the compact object is an accreting neutron star .
The observed spectrum and spectral variability can be explained if the compact object in the system is a rotation powered pulsar .