  We investigate associated production of selectrons and the lightest
neutralino (LSP) in the process e^- + gamma --> neutralino_1 + selectron_{L/R}
with the selectron subsequently decaying into an electron and the LSP. Total
cross sections and various polarization asymmetries are calculated for photons
produced by Compton backscattering of a polarized laser beam at an $e^+e^-$
linear collider with CMS energy $\sqrt{s_{ee}}=500$ GeV and with polarized
beams. The total cross section and in particular the polarization asymmetries
show a characteristic dependence on the gaugino mass parameter $M_1$. Therefore
this process is suitable for testing the GUT relation
$M_1=M_2\cdot{5/3}\tan^2\theta_W $.
