The rigidity dependence of galactic and anomalous cosmic rays is studied for the four step decreases that define the long-term modulation of solar cycle 21. The data are from cosmic ray experiments on IMP 8, ISEE 3, Voyager 1, and Pioneer 10. For the first three step decreases the diffusion coefficient &kgr; is proportional to the particle rigidity R. For the fourth modulation event that occurs during the recovery phase of the long-term modulation, &kgr; is proportional to R0.4. For the three step decreases where simultaneous galactic cosmic ray ion and electron data are available at 1 AU, the same modulation function is obtained for both positively and negatively charged particles, suggesting that gradient and curvature drift effects are not an important element of these modulation events. The modulation functions for anomalous helium and oxygen from the Pioneer 10 and Voyager 1 experiments are identical to that of galactic cosmic rays and are consistent with the expected singly charged state of this component. At heliocentric distances beyond some 15 AU, &kgr;⊥ is expected to dominate over &kgr;∥. However, there is no significant change in the modulation function with increasing heliocentric distance suggesting that in general &kgr;∥ and &kgr;⊥∝R. ¿ American Geophysical Union 1995