We report the dielectric response (100mHz-1MHz) of the spin density wave (S
DW) in (TMTSF)(2)PF6 and (TMTSF)(2)AsF6 between 1.4K-4.2K. The relaxation g
radually slows down in PF6, while in AsF6 it shows a tendency of divergence
hinting the appearance of a glassy transition. The latter correlates with
the important increase of the electrical threshold field for the SDW slidin
g found in AsF6, but not observed in PF6 compound.