  We investigate the star formation history of both the bright star clusters
and the diffuse `field star' population in the dwarf starburst galaxy NGC 5253
using STIS longslit ultraviolet spectroscopy. Our slit covers a physical area
of 370 x 1.6 pc and includes 8 apparent clusters and several inter-cluster
regions of diffuse light which we take to be the field. The diffuse light
spectrum lacks the strong O-star wind features which are clearly visible in
spectra of the brightest clusters. This discrepancy provides compelling
evidence that the diffuse light is not reflected light from nearby clusters,
but originates in a UV-bright field star population, and it raises the issue of
whether the star formation process may be operating differently in the field
than in clusters. We compare our spectra to STARBURST99 evolutionary synthesis
models which incorporate a new low metallicity atlas of O-star spectra. We
favor a scenario which accounts for the paucity of O-stars in the field without
requiring the field to have a different IMF than the clusters: stellar clusters
form continuously and then dissolve on ~10 Myr timescales and disperse their
remaining stars into the field. We consider the probable contribution of an
O-star deficient field population to the spatially unresolved spectra of high
redshift galaxies. (Abridged)
