  We present Spitzer observations of the blue compact dwarf galaxy (BCD) Haro
3, with an oxygen abundance of 12+log(O/H)=8.32. These data are part of a
larger study of star formation and dust in low-metallicity environments.The IRS
spectrum of Haro 3 shows strong narrow Polycyclic Aromatic Hydrocarbon (PAH)
emission, with high equivalent widths. Gaseous nebular fine-structure lines are
also seen. Despite the absence of optical high-excitation lines, a faint
high-ionization [O IV] line at 25.89 micron indicates the presence of radiation
as hard as 54.9 eV. A CLOUDY model suggests that the MIR lines originate in two
regions: a low-extinction optically-emitting region, and an optically invisible
one with much higher extinction. The morphology of Haro 3 changes with
wavelength. IRAC 4.5 micron traces extended stellar photospheric emission from
the body of the galaxy and hot dust continuum coming mainly from star-forming
regions; 8 micron probes extended PAH emission coming mainly from the general
ISM; MIPS 24 and 70 micron images map compact small-grain warm dust emission
associated with active star formation, and 160 micron reflects cooler extended
dust associated with older stellar populations. We have derived the
optical-to-radio spectral energy distribution (SED) of the brightest
star-forming region A in Haro 3. The best-fit DUSTY model of the SED gives a
total luminosity of 2.8e9 Lsun and a mass of 2.8e6 Msun for the ionizing
clusters. We infer an extinction A(V)<3, intermediate between the optical
A(V)~0.5 and the radio A(V)~8, consistent with the picture that longer
wavelength observations probe more deeply into star-forming regions.
