Cook pasta according to package directions. In a small skillet, saute the green pepper, onion and garlic in oil and butter until almost tender. Stir in the clam juice, basil, salt, pepper and red pepper flakes. Bring to a boil. Reduce heat; simmer, uncovered, for 5-7 minutes. Stir in clams; heat through. Drain pasta; transfer to a bowl. Pour sauce over pasta; toss to coat.