  The KTeV experiment at Fermilab has isolated a total of 132 events from the
rare decay KL->e+e-mu+mu-, with an estimated background of 0.8 events. The
branching ratio of this mode is determined to be 2.69 +/- 0.24 (stat) +/- 0.12
(syst) x 10^-9, with a radiative cutoff of M(eemm)^2/M(K)^2 > 0.95. The first
measurement using this mode of the parameter alpha from the D'Ambrosio,
Isidori, and Portoles model of the KLg*g* vertex yields a result of -1.59 +/-
0.37, consistent with values obtained from other decay modes. Because of the
limited statistics, no sensitivity is found to the DIP parameter beta. The
magnitude of the angular distribution asymmetry between the e+e- and mu+mu-
planes, indicative of a CP-violating contribution to the decay, is found to be
consistent with zero. We set a 90% C.L. upper limit of 4.12 x 10^(-11) on the
branching ratio of the lepton flavor--violating mode KL->e+-e+-mu+-mu+-, a
factor of three improvement over the current limit from the KTeV experiment.
