Cook linguine to desired doneness as directed on package. Drain; rinse with hot water. Toss linguine with sour cream and
2 tablespoons margarine. Cover to keep warm.
Meanwhile, in large skillet over medium heat saute onions and garlic in 2 tablespoons margarine until onion is tender. Stir in shrimp, clams, chicken broth, wine, lemon juice, parsley and seasonings. Bring to a boil; reduce heat and simmer 5 minutes.
In small bowl, combine cornstarch and water; blend well. Slowly stir into seafood mixture. Cook until mixture thickens, stirring constantly. Serve seafood sauce over linguine.