Heat olive oil in medium-size saucepan. saut� onions and garlic until onions are transparent and garlic is slightly browned. Add red and yellow peppers and sau t� for about 5 minutes, or until peppers begin to soften. Set aside. In a large, heavy bottomed pot, brown sausages, one pound at a time, cooking each batch approximately 20 minutes. Remove from pot, drain on paper towel, and cut into 1 /4-inch slices. Remove all but 1 tablespoon of fat from pot and, over medium he at, stir in white wine, mixing well with scrapings from bottom of the pot. Add onion, garlic and pepper mixture. Stir in plum tomatoes, oregano, black pepper, crushed red-pepper flakes and sausage slices. Simmer uncovered for 25 minutes. Boil water for rigatoni and begin cooking it. In the last 8 minutes of the coo king time for the sauce, add asparagus and continue to simmer 8 minutes, or unt il asparagus is tender. Drain rigatoni and serve with sauce.