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Many open questions in X-ray astronomy are limited by the relatively smallnumber of objects in uniform optically-identified samples, especially when raresubclasses are considered, or subsets isolated to search for evolution orcorrelations between wavebands. We describe initial results of a program aimedto ultimately yield 10^4 X-ray source identifications--a sample about an orderof magnitude larger than earlier efforts. The technique employs X-ray data fromthe ROSAT All-Sky Survey (RASS), and optical imaging and spectroscopic followupfrom the Sloan Digital Sky Survey (SDSS). Optical objects in the SDSS catalogsare automatically cross-correlated with RASS X-ray source positions; thenpriorities for follow-on SDSS optical spectra of candidate counterparts areautomatically assigned using an algorithm based on the known fx/fopt ratios forvarious classes of X-ray emitters. SDSS parameters for optical morphology,magnitude, colors, plus FIRST radio data, serve as proxies for object class.  Initial application of this approach to 1400 deg^2 of sky provides a catalogof 1200 spectroscopically confirmed quasars/AGN that are probable RASSidentifications. Most of the IDs are new, and only a few percent of the AGN arelikely to be random superpositions. The magnitude and redshift ranges of thecounterparts extend over 15<m<21 and 0.03<z<3.6. Although most IDs are quasarsand Sy 1s, a variety of other AGN subclasses are also sampled. Substantialnumbers of rare AGN are found, including more than 130 narrow-line Seyfert 1sand 45 BL Lac candidates. These results already provide a sizeable set of newIDs, show utility of the sample in multi-waveband studies, and demonstrate thecapability of the RASS/SDSS approach to efficiently proceed towards the largesthomogeneously selected/observed sample of X-ray emitting AGN. Abridged AbstractComment: 39 pages, 11 bitmapped figs (PDF view or print OK). Version accepted  by AJ: slightly expanded sample, 1 new fig, minor modification

A Large, Uniform Sample of X-Ray-emitting AGNs: Selection Approach and an Initial Catalog from theROSATAll-Sky and Sloan Digital Sky Surveys