  We consider decelerating and cooling an ensemble of multilevel atoms and
molecules with a coherent train of ultrashort laser pulses. In the frequency
domain such trains form frequency combs. We propose a novel see-saw scheme of
Doppler cooling of multilevel atoms and molecules. In this scheme the teeth of
the frequency comb are periodically moved in and out of resonance with the
allowed transitions. The see-saw cooling may be carried out in practice by
switching carrier-envelope phase offset between predefined values. We study the
performance of the see-saw scheme for the simplest prototype three-level
$\Lambda$ system and demonstrate its advantage. For these systems we
demonstrate a procedure for determining optimal train parameters, and see-saw
switching period. We also illustrate the performance of the protocol by
numerically simulating time evolution of velocity distribution.
