We propose sensitive high resolution imaging of mid-infrared continuum
and 12.8 micron [Ne II] line emission in three IR luminous galaxies
with extended CO distribution (VV 114, Mrk 273, NGC 7674) using the
ISO infrared camera (ISOCAM).  The aim of this study is to trace the
extent of the starburst activity in relation to the extended massive
molecular complexes traced in CO and to test if these galaxies are the
transitional objects in the early stages of evolving into the
ultraluminous phase like Arp 220.  We need the high angular resolution
(~5") achievable with ISOCAM in order to learn how the fuel (molecular
gas traced in CO) and star forming activity are spatially related in
these presumably young starburst galaxies.  We also need the ability to
probe deeply into highly obscured regions of massive star formation
because both CO and near-IR observations imply high extinction toward
the central regions of these galaxies.  The mid-infrared continuum
emission is used to trace the youngest stars (heating the dust) while
the [Ne II] observations trace the hot gas associated with the star
forming activity, independent of variations in the dust properties.
Our proposed ISOCAM observations should reveal how the star formation
proceeds and shapes these systems during the early stages of their
evolution.