Dalitz plots of 74 000 Ke30 and 150 000 Kμ30 decays have been investigated to measure the t-dependence of the form factors ƒ+(t) and ƒ(t) describing the vector contribution to the decay matrix element. The decays were registered by a wire spark chamber spectrometer in the neutral beam of the Serpukhov accelerator. An analysis using a linear expansion of the form factors gives the slopes: λe+=0.0306±0.0034 for the Ke30 decays and λμ+ = 0.0427±0.0044, λ0 = 0.0341± 0.0067 for the Kμ30 decays. The ratio of the form factors ƒ−to ƒ+ has been found to be ξ(0)=ƒ−(0)/ƒ+(0)=−0.10±0.09. These results are compared with the relevant theoretical models. Together with the data of other experiments in which the parameters of muon and electron interactions are measured, the observed difference between λ+μ and λ+e gives some indication of the violation of μ-e universality.