  We present HST WFPC2 observations in three bands (F450W, F467M and F814W) of
a group of three galaxies at z=2.8 discovered in a ground-based narrow-band
search for Lyman alpha emission near the z=2.8 quasar PKS0528-250. One of the
galaxies is a damped (DLA) absorber and these observations bear on the relation
between the DLA clouds and the Lyman-break galaxies and the stage in the
evolution of galaxies they represent. We describe a procedure for combining the
undersampled WFPC2 images pointed on a sub-pixel grid, which largely recovers
the full sampling of the WFPC2 point spread function (psf). These three
galaxies have similar properties to the Lyman-break galaxies except that they
have strong Lyman alpha emission. The three galaxies are detected in all three
bands, with average B~26, I~25. Two of the galaxies are compact with intrinsic
(i.e. after correcting for the effect of the psf) half-light radii of ~0.1
arcsec (~0.4/h kpc, q_o=0.5). The third galaxy comprises two similarly compact
components separated by 0.3 arcsec. The HST images and a new ground-based Lyman
alpha image of the field provide evidence that the three galaxies are more
extended in the light of Lyman alpha than in the continuum. The measured impact
parameters for this DLA galaxy (1.17 arcsec), for a second confirmed system,
and for several candidates, provide a preliminary estimate of the
cross-section-weighted mean radius of the DLA gas clouds at z~3 of less than
13/h kpc, for q_o=0.5. Given the observed sky covering factor of the absorbers
this implies that for q_o=0.5 the space density of DLA clouds at these
redshifts is more than five times the space density of spiral galaxies locally,
with the actual ratio probably considerably greater. For q_o=0.0 there is no
evidence as yet that DLA clouds are more common than spiral galaxies locally.
