  In this paper we present the longest exposure (97 ks) XMM-Newton EPIC-pn
spectrum ever obtained for the Seyfert 1.5 galaxy 1H 0419-577. With the aim of
explaining the broadband emission of this source, we took advantage of the
simultaneous coverage in the optical/UV that was provided in the present case
by the XMM-Newton Optical Monitor and by a HST-COS observation. Archival FUSE
flux measurements in the FUV were also used for the present analysis. We
successfully modeled the X-ray spectrum together with the optical/UV fluxes
data points using a Comptonization model. We found that a blackbody temperature
of $T \sim 56$ eV accounts for the optical/UV emission originating in the
accretion disk. This temperature serves as input for the Comptonized components
that model the X-ray continuum. Both a warm ($T_{\rm wc} \sim 0.7 $ keV,
$\tau_{\rm wc} \sim 7 $) and a hot corona ($T_{\rm hc} \sim 160 $ keV,
$\tau_{\rm hc} \sim 0.5$) intervene to upscatter the disk photons to X-ray
wavelengths. With the addition of a partially covering ($C_v\sim50\%$) cold
absorber with a variable opacity ($ {\it N}_{\rm H}\sim [10^{19}- 10^{22}]
\,\rm cm^{-2}$), this model can well explain also the historical spectral
variability of this source, with the present dataset presenting the lowest one
(${\it N}_{\rm H}\sim 10^{19} \, \rm cm^{-2} $). We discuss a scenario where
the variable absorber, getting ionized in response to the variations of the
X-ray continuum, becomes less opaque in the highest flux states. The lower
limit for the absorber density derived in this scenario is typical for the
broad line region clouds. Finally, we critically compare this scenario with all
the different models (e.g. disk reflection) that have been used in the past to
explain the variability of this source
