  We present V and I photometry of the resolved stars in the cometary blue
compact dwarf galaxy UGC 4483 using Hubble Space Telescope Wide Field Planetary
Camera 2 (WFPC2) images. The resulting I vs. (V-I) color-magnitude diagram
(CMD) reaches limiting magnitudes V = 27.5 mag and I = 26.5 mag for photometric
errors less than 0.2 mag. It reveals not only a young stellar population of
blue main-sequence stars and blue and red supergiants, but also an older
evolved population of red giant and asymptotic giant branch stars. The measured
magnitude I = 23.65 +/- 0.10 mag of the red giant branch tip results in a
distance modulus (m-M) = 27.63 +/- 0.12, corresponding to a distance of 3.4 +/-
0.2 Mpc. The youngest stars are associated with the bright H II region at the
northern tip of the galaxy. The population of older stars is found throughout
the low-surface-brightness body of the galaxy and is considerably more spread
out than the young stellar population, suggesting stellar diffusion. The most
striking characteristics of the CMD of UGC 4483 are the very blue colors of the
red giant stars and the high luminosity of the asymptotic giant branch stars.
Both of these characteristics are consistent with either: 1) a very low
metallicity ([Fe/H] = -2.4 like the most metal-deficient globular clusters) and
an old age of 10 Gyr, or 2) a higher metallicity ([Fe/H] = -1.4 as derived from
the ionized gas emission lines) and a relatively young age of the oldest
stellar population in UGC 4483, not exceeding ~ 2 Gyr. Thus our data do not
exclude the possibility that UGC 4483 is a relatively young galaxy having
formed its first stars only ~ 2 Gyr ago.
