  Events containing a pair of charged leptons and significant missing
transverse momentum are selected from a data sample corresponding to a total
integrated luminosity of 20.6 pb^-1 at centre-of-mass energies of 161 GeV and
172 GeV. The observed number of events, four at 161 GeV and nine at 172 GeV, is
consistent with the number expected from Standard Model processes,
predominantly arising from W+W- production with each W decaying leptonically.
This topology is also an experimental signature for the pair production of new
particles that decay to a charged lepton accompanied by one or more invisible
particles. Further event selection criteria are described that optimise the
sensitivity to particular new physics channels. No evidence for new phenomena
is observed and limits on the production of scalar charged lepton pairs and
other new particles are presented.
