Heat the orange juice to lukewarm and add 1-1/2 teaspoons of margarine to melt.

Meanwhile, mix the yeast with the sugar. Stir in the lukewarm water; let the yeast mixture soften.

Place the white and rye flours, the salt, and ground fennel in a large bowl. With your fist, make a well in the center of the dry ingredients. Combine the yeast and orange juice mixtures and pour into the well. Stir thoroughly for several minutes until the dough becomes quite stiff. Cover the bowl and allow the dough to rise until double in bulk (approximately 1 hour).

Cream until smooth the 2 tablespoons of margarine and light brown sugar. With the back of a large spoon, work this mixture into the dough after it has risen. Knead until the margarine-sugar mixture has been thoroughly incorporated into the dough. Break up the dough into about 25 equal pieces. Roll each piece into a ball between the palms, place on lightly oiled baking sheets, and press each down slightly. Cover the baking sheets and allow the balls to rise in a warm, draft-free place until they double in size (about 20 minutes). Do not turn on the oven until the baking sheets are arranged on the oven racks.

Bake at 400°F for 12 minutes. Reduce the temperature to 350°F and bake the rusks 15 minutes more. Remove from the oven and cool on wire racks. When cool, slice them in half. Toast the rusks to a golden brown for 15 minutes in an oven preheated to 275°F. After cooling once more, store in tight containers.