Place corn with husks in cold water; soak 30 minutes. Combine chili powder, salt, cumin, and butter in a small bowl. Pull husks back; scrub silks from corn.
Brush chili powder mixture over corn. Wrap husks around corn.
Prepare grill or broiler.
Place corn on a grill rack or broiler pan; cook 20 minutes or until corn is lightly browned, turning every 5 minutes.