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[Abridged] Context: Radiation-driven mass loss plays a key role in thelife-cycles of massive stars. However, basic predictions of such mass lossstill suffer from significant quantitative uncertainties. Aims: We develop newradiation-driven, steady-state wind models for massive stars with hot surfaces,suitable for quantitative predictions of global parameters like mass-loss andwind-momentum rates. Methods: The simulations presented here are based on aself-consistent, iterative grid-solution to the spherically symmetric,steady-state equation of motion, using full NLTE radiative transfer solutionsin the co-moving frame to derive the radiative acceleration. We do not rely onany distribution functions or parametrization for computation of the line forceresponsible for the wind driving. Results: In this first paper, we presentmodels representing two prototypical O-stars in the Galaxy, one with a higherstellar mass M/Msun=59 and luminosity log10(L/Lsun)= 5.87 and one with a lowerM/Msun= 27 and log10(L/Lsun)= 5.1. For these simulations, basic predictions forglobal mass-loss rates and velocity laws are given, and the influence fromadditional parameters like wind clumping and microturbulent speeds discussed. Akey result is that our mass-loss rates are significantly lower than thosepredicted by the mass-loss recipes normally included in models of massive-starevolution. Conclusions: Our results support previous suggestions that GalacticO-star mass-loss rates may be overestimated in present-day stellar evolutionmodels, and that new rates thus might be needed. Indeed, future papers in thisseries will incorporate our new models into such simulations of stellarevolution, extending the very first simulations presented here toward largergrids covering a range of metallicities, B supergiants across the bistabilityjump, and possibly also Wolf-Rayet stars.

New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars. I. Method and first results