Mixture containing an organometallic compound of alkali metal and stabilized toward the effects of an air atmosphere, and consisting of 1 to 60 wt. % of an organic polymer of molecular weight of at least 4000 obtained by polymerization of ethylene or ethylene substituted with at least one alkyl group with 1 to 3 carbon atoms, phenyl, or an alkoxy group with 1 to 10 carbon atoms in the straight or branched chain, or a polymer obtained by polymerization of ethylene oxide or propylene oxide, or a mixture of the above mentioned polymers, the product of interaction of 1 mol of alkali metal selected from the group consisting of lithium, sodium and potassium and 0.4 to 2 mol of a hydrocarbon containing 2 to 4 aromatic nuclei, 500 to 5000 ml of an organic solvent or a mixture of solvents selected from the group comprising aliphatic or cycloaliphatic ethers, 0 to 50 wt. % of an aromatic, aliphatic or cycloaliphatic hydrocarbon, and 0 to 1 mol of the macrocyclic polyether (crown ether) of the general formula ##STR3## where m + n = 2 to 10.