Soak the rice in water to cover for 4 hours. Drain and pat dry. Soak the mushrooms in 1/2 cup warm water for 1 hour. Drain and discard the tough stems. Chop the caps finely.
Mix together all the ingredients, except the rice, until well blended. Your hands are best for this job. Form balls 1 inch in diameter.
Spread the rice on a baking sheet. One at a time, roll the pearl balls in it, coating completely. Set the balls on a baking sheet lined with waxed paper. Refrigerate. The balls can be frozen at this point.
To steam pearl balls, put steamer in a pan or wok and add water so that it comes to within 1 inch of steamer bottom. Put balls on steamer racks. Bring to boil. Cover and steam for 30 minutes. Serve hot.