  Bethe-Salpeter equation for the massive particles with spin 1 is considered.
The scattering amplitude decomposition of the particles with spin 1 by
relativistic tensors is derived. The transformation coefficients from helicity
amplitudes to invariant functions is found. The integral equations system for
invariant functions is obtained and partial decomposition of this system is
performed. Equivalent system of the integral equation for the partial helicity
amplitudes is presented.
