Drain clams, reserving juice; set aside. In a small skillet, saute onion in 1 tablespoon butter until tender. Stir in flour until blended. Gradually add the horseradish, garlic powder, Worcestershire sauce, salt and reserved clam juice. Bring to a boil; cook and stir for 2 minutes or until thickened.
Remove from heat; stir in clams.
Flatten bread with a rolling pin. Melt remaining butter; brush one side of each slice of bread.
Spread with clam mixture; roll up.
Brush with remaining butter; sprinkle with paprika.
Cut rolls into thirds; place on a greased baking sheet.
Bake at 425° for 5-8 minutes or until lightly browned.