Pair effective ion—ion interactions, free energy, pressure, and electrical resistance of liquid metallic helium are calculated in a wide range of densities and temperatures. For this problem, a perturbation theory by the pseudopotential of the electron—ion interaction is used. In all cases, calculations are carried out with regard to terms of the third-order perturbation theory, which is the maximum possible accuracy of calculations today. As pseudopotential, the one-parameter model pseudopotential is taken into account. For conduction electrons, the random phase approximation is used. Their exchange interaction and correlation are taken into account in local field approximation. For ionic subsystem, the model of hard spheres is used. Their diameter is one of the fitting parameters of a theory. This diameter and density, at which the transition from one-valent metallic helium to the divalent state takes place, are obtained from the analysis of the effective pair ion—ion interaction. The case of the one-valent metal helium is considered in detail. In all the above cases, the role of the third-order terms is significant. The value of electrical resistivity of metallic helium corresponds to the characteristic value of elementary one-valent metals. The behaviour of pressure as a function of density and temperature has the same peculiarity. The investigated ranges of densities and temperatures correspond to conditions observed in the central part of the gas-giants. Analysis of the results indicates the possible existence of the helium in a metallic state in the central parts of the Jovian-group planets.