  A search for associated production of charginos and neutralinos is performed
using data recorded with the D0 detector at a ppbar center-of-mass energy of
1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final
states with missing transverse energy and three leptons, of which at least two
are electrons or muons. No evidence for supersymmetry is found in a dataset
corresponding to an integrated luminosity of 320 pb-1. Limits on the product of
the production cross section and leptonic branching fraction are set. For the
minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95%
C.L. is derived in regions of parameter space with enhanced leptonic branching
fractions.
