In ceramic La_1-3Ca_xMnO₃ samples with 0 ≤ x ≤ 0.15 and the concentration of holes c = 0.18-0.22 between T = 77 and 340 K the resistivity, ρ, is shown to have an activated character both above and below the ferromagnetic Curie temperature, T_C. The temperature dependence of the local activation energy, E_loc (T) = d 1n ρ(T)/d(kT)^-1 gives evidence for a variable-range hopping conductivity over states of the Coulomb gap. The width of the gap Δ ≈ 0.24eV, the effective dielectric permeability κ ≈ 3.6 and the carrier localization radius ξ ≈ 5.1 angstrom in the paramagnetic phase are determined. The value of ξ suggests hopping of small lattice polarons at T > T_C. With decreasing temperature two successive transitions, at temperatures T′_C and T″_C, associated with divergence of the correlation length, are observed in the vicinity of T_C. They can be interpreted in terms of critical increase (as T approaches T′_C from higher temperatures) and decrease (when T shifts from T″_C towards lower temperatures) of the radius of magnetic polarons, generated by a small fraction of the lattice polarons as T → T_C. The difference between T_C and the temperature of the first divergence of ξ, T′_C < T_C, gives evidence of percolative character of the FM-PM transition.