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We detect the 21 cm line of neutral hydrogen in absorption at a redshift of0.673 towards the 1 Jy radio source 1504+377. The 1504+377 radio source islocated toward the center of what appears to be an inclined disk galaxy at z =0.674. The 21 cm absorption line shows multiple velocity components over avelocity range of about 100 km sec$^{-1}$, with a total HI column density:N(HI) = $3.8\times10^{19}\times({{T_s}\over{f}})$ cm$^{-2}$. Thevelocity-integrated optical depth of this system is the largest yet seen forredshifted HI 21 cm absorption line systems (Carilli 1995). The 21 cmabsorption line is coincident in redshift with a previously detected broadmolecular absorption line system (Wiklind and Combes 1996). We do not detect HI21 cm absorption associated with the narrow molecular absorption line system atz = 0.67150, nor do we detect absorption at these redshifts by the 18 cm linesof OH, nor by the 2 cm transition of H$_2$CO. There is no evidence for a brightoptical AGN in 1504+377, suggesting significant obscuration through the disk --a hypothesis supported by the strong absorption observed. The 1504+377 systemresembles the ``red quasar'' PKS 1413+135, which has been modeled as aoptically obscured AGN with a very young radio jet in the center of a gas richdisk galaxy (Perlman et al. 1996). The presence of very bright radio jets atthe centers of these two disk galaxies presents a challenge to unificationschemes for extragalactic radio sources and to models for the formation ofradio loud AGN.Comment: 17 pages, postscrip

Neutral Hydrogen 21 Centimeter Absorption at Redshift 0.673 toward 1504+377