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We present the first results of a spectroscopic survey of Lyman breakgalaxies in the near-infrared aimed at detecting the emission lines of [O II],[O III], and Hbeta from the H II regions of star forming galaxies at z = 3.  From observations of 19 objects with the Keck and VLT telescopes, we reachthe following main conclusions. Contrary to expectations, the star formationrates deduced from the Hbeta luminosity are on average no larger than thoseimplied by the stellar continuum at 1500 A; presumably any differentialextinction between rest-frame optical and UV is small compared with therelative uncertainties in the calibrations of these two star formation tracers.For the galaxies in our sample, the abundance of O can only be determined towithin one order of magnitude. Even so, it seems well established that LBGs arethe most metal-enriched structures at z = 3, apart from QSOs, with abundancesgreater than about 1/10 solar. They are also significantly overluminous fortheir metallicities; this is probably an indication that their mass-to-lightratios are small compared with present-day galaxies. At face value theirvelocity dispersions, sigma = 50 - 115 km/s imply virial masses of about10^{10} solar masses within half-light radii of 2.5 kpc. However, we are unableto establish if the widths of the emission lines do reflect the motions of theH II regions within the gravitational potential of the galaxies, even though intwo cases we see hints of rotation curves. All 19 LBGs observed show evidencefor galactic-scale superwinds; such outflows are important for regulating starformation, distributing metals over large volumes, and allowing Lyman continuumphotons to escape and ionize the IGM.Comment: 44 pages, LaTeX, 13 Postscript Figures. Accepted for publication in  the Astrophysical Journal, Vol. 554, No. 2 (Jun 20, 2001

The Rest‐Frame Optical Spectra of Lyman Break Galaxies: Star Formation, Extinction, Abundances, and Kinematics