[en] Studies aimed at the nature of magnetic interactions in Fe and Cr substituted lanthanum deficient manganites, La_0.88Mn_1-xFe_xO₃ (x=0-0.15) and La_0.88Mn_1-yCr_yO₃ (y=0-0.175) are reported. The oxides order ferromagnetically for the entire range of x- and y-values. A decrease in the Curie temperature T_c with increasing substitution is observed for both compounds, but the decrease in T_c is large for Fe substitution. A large decrease was also seen in the low-temperature magnetic moment of Fe substituted samples. The data indicate possible ferromagnetic ordering of Cr and antiferromagnetic ordering of Fe moments in the oxides. Ferromagnetic resonance studies indicate (i) strong spin-lattice effects in the paramagnetic state, (ii) valence-exchange effects in the ferromagnetic state, and (iii) possible microscopic inhomogeneities in Cr-substituted samples