In large saucepan, heat oil over medium heat. Add onion; saute until slightly softened, about 5 minutes. Add garlic; saute 2 minutes (do not let garlic brown).
Stir sugar, salt, pepper, basil, oregano, tomato sauce and tomato paste into onion mixture until well blended. Add the plum tomatoes. Stir in clam juice. Simmer, covered, 30 minutes. Then simmer, uncovered, for 10 minutes.
Meanwhile, cook pasta in large pot of lightly salted boiling water until al dente, firm yet tender.
While the pasta is cooking, puree tomato mixture with hand blender or in a regular blender. Return sauce to saucepan. Stir in clams and reserved 1/4 cup clam juice; gently heat through, 2 to 3 minutes.
Drain the pasta well; transfer to a serving platter. Measure out 4 cups of the sauce and toss with the pasta.
Refrigerate remaining 4 cups sauce, tightly covered, for up to 2 days for another dinner, or freeze for up to 3 months.