  Motivated by the discovery of young, massive stars in the nuclei of some
LINER/H II ``transition'' nuclei such as NGC 4569, we have computed
photoionization models to determine whether some of these objects may be
powered solely by young star clusters rather than by accretion-powered active
nuclei. The models were calculated with the photoionization code CLOUDY, using
evolving starburst continua generated by the the STARBURST99 code of Leitherer
et al. (1999). We find that the models are able to reproduce the emission-line
spectra of transition nuclei, but only for instantaneous bursts of solar or
higher metallicity, and only for ages of ~3-5 Myr, the period when the
extreme-ultraviolet continuum is dominated by emission from Wolf-Rayet stars.
For clusters younger than 3 Myr or older than 6 Myr, and for models with a
constant star-formation rate, the softer ionizing continuum results in an
emission spectrum more typical of H II regions. This model predicts that
Wolf-Rayet emission features should appear in the spectra of transition nuclei.
While such features have not generally been detected to date, they could be
revealed in observations having higher spatial resolution. Demographic
arguments suggest that this starburst model may not apply to the majority of
transition nuclei, particularly those in early-type host galaxies, but it could
account for some members of the transition class in hosts of type Sa and later.
The starburst models during the Wolf-Rayet-dominated phase can also reproduce
the narrow-line spectra of some LINERs, but only under conditions of
above-solar metallicity and only if high-density gas is present (n_e >~ 10^5
cm^{-3}). This scenario could be applicable to some ``Type 2'' LINERs which do
not show any clear signs of nonstellar activity.
