Methylates (mono- and asymmetric dimethylation) the guanidino nitrogens of arginyl residues in proteins. May methylate histone H3 at 'Arg-17' and activate transcription via chromatin remodeling (By similarity). L-arginyl-[protein] + 2 S-adenosyl-L-methionine = 2 H(+) + N(omega),N(omega)-dimethyl-L-arginyl-[protein] + 2 S-adenosyl-L-homocysteine Homodimer. The dimethylated protein is the major form. Belongs to the class I-like SAM-binding methyltransferase superfamily. Protein arginine N-methyltransferase family.