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We discuss the optical and radio properties of 30,000 FIRST sourcespositionally associated with an SDSS source in 1230 deg$^2$ of sky. Themajority (83%) of the FIRST sources identified with an SDSS source brighterthan r=21 are optically resolved. We estimate an upper limit of 5% for thefraction of quasars with broad-band optical colors indistinguishable from thoseof stars. The distribution of quasars in the radio flux -- optical flux planesupports the existence of the "quasar radio-dichotomy"; 8% of all quasars withi<18.5 are radio-loud and this fraction seems independent of redshift andoptical luminosity. The radio-loud quasars have a redder median color by 0.08mag, and a 3 times larger fraction of objects with red colors. FIRST galaxiesrepresent 5% of all SDSS galaxies with r<17.5, and 1% for r<20, and aredominated by red galaxies. Magnitude and redshift limited samples show thatradio galaxies have a different optical luminosity distribution than non-radiogalaxies selected by the same criteria; when galaxies are further separated bytheir colors, this result remains valid for both blue and red galaxies. Thedistributions of radio-to-optical flux ratio are similar for blue and redgalaxies in redshift-limited samples; this similarity implies that thedifference in their luminosity functions, and resulting selection effects, arethe dominant cause for the preponderance of red radio galaxies in flux-limitedsamples. We confirm that the AGN-to-starburst galaxy number ratio increaseswith radio flux, and find that radio emission from AGNs is more concentratedthan radio emission from starburst galaxies (abridged).Comment: submitted to AJ, color gif figures, PS figures available from  ivezic@astro.princeton.ed

Optical and Radio Properties of Extragalactic Sources Observed by the FIRST Survey and the Sloan Digital Sky Survey