  Context. We report the detection by the AGILE satellite of an intense
gamma-ray flare from the gamma-ray source 3EG J1255-0549, associated to the
Flat Spectrum Radio Quasar 3C 279, during the AGILE pointings towards the Virgo
Region on 2007 July 9-13.
  Aims. The simultaneous optical, X-ray and gamma-ray covering allows us to
study the spectral energy distribution (SED) and the theoretical models
relative to the flaring episode of mid-July.
  Methods. AGILE observed the source during its Science Performance
Verification Phase with its two co-aligned imagers: the Gamma- Ray Imaging
Detector (GRID) and the hard X-ray imager (Super-AGILE) sensitive in the 30 MeV
- 50 GeV and 18 - 60 keV respectively. During the AGILE observation the source
was monitored simultaneously in optical band by the REM telescope and in the
X-ray band by the Swift satellite through 4 ToO observations.
  Results. During 2007 July 9-13 July 2007, AGILE-GRID detected gamma-ray
emission from 3C 279, with the source at ~2 deg from the center of the Field of
View, with an average flux of (210+-38) 10^-8 ph cm^-2 s^-1 for energy above
100 MeV. No emission was detected by Super-AGILE, with a 3-sigma upper limit of
10 mCrab. During the observation lasted about 4 days no significative gamma-ray
flux variation was observed.
  Conclusions. The Spectral Energy Distribution is modelled with a homogeneous
one-zone Synchrotron Self Compton emission plus the contributions by external
Compton scattering of direct disk radiation and, to a lesser extent, by
external Compton scattering of photons from the Broad Line Region.
