  We present the first high spectral resolution X-ray observation of the
broad-line radio galaxy 3C 390.3 obtained with the high energy transmission
grating (HETG) spectrometer on board the Chandra X-ray Observatory. The
spectrum shows complex emission and absorption features in both the soft X-rays
and Fe K band. We detect emission and absorption lines in the energy range
between E = 700-1000 eV associated with ionized Fe L transitions (Fe XVII-XX).
An emission line at the energy of E=6.4 keV consistent with the Fe K\alpha is
also observed. Our best-fit model requires at least three different components:
(i) a hot emission component likely associated with the hot interstellar medium
in this elliptical galaxy with temperature kT=0.5+/-0.1 keV; (ii) a warm
absorber with ionization parameter log\xi=2.3+/-0.5 erg s^{-1} cm, column
density logN_H=20.7+/-0.1 cm^{-2}, and outflow velocity of v_{out}<150 km
s^{-1}; (iii) a lowly ionized reflection component in the Fe K band likely
associated with the optical broad line region or the outer accretion disk.
These evidences suggest the possibility that we are looking directly down the
ionization cone of this active galaxy and that the central X-ray source only
photoionizes along the unobscured cone. This is overall consistent with the
angle-dependent unified picture of active galactic nuclei.
