  AIMS : To characterize the molecular environment of classical T Tauri stars
in Lupus observed with the Spitzer Space Telescope and to search for gas-rich
disks toward these sources.
  METHODS : Submillimeter observations of 12CO, 13CO and C18O in the J=3-2 and
2-1 lines were obtained with the James Clerk Maxwell Telescope toward a sample
of 21 T Tauri stars with disks in the Lupus molecular clouds. Pointings at the
sources and at selected off-positions are presented in order to disentangle
material associated with disks from ambient cloud material.
  RESULTS : One source, IM Lup (Sz 82), has been found with double-peaked 12CO
and 13CO profiles characteristic of a large rotating gas disk. The inclination
of the disk is found to be ~20 degrees, with an outer radius of 400-700 AU. For
most other sources, including GQ Lup with its substellar companion, the
single-dish 12CO lines are dominated by extended cloud emission with a complex
velocity structure. No evidence for molecular outflows is found. Compact C18O
emission due to dense circumstellar material has been detected toward only two
sources. Future searches for gas-rich disks in Lupus should either use
interferometers or perform very deep single-dish integrations in dense gas
tracers to separate the cloud and disk emission.
