Cut off the root ends of the leeks and trim the tough green tops of the leaves. Cut the leeks into about 2-inch lengths then slice into narrow julienne strips. Place the cut leeks in a large bowl and cover with cold water. If they are very sandy, remove them, discard the dirty water and cover again with fresh water. Put 2 tablespoons of the olive oil and the leeks in a saute pan or skillet large enough to hold the fish fillets in a single layer and place it over medium-low heat. Add enough water to come about 1/2" up the side of pan and season lightly with salt and pepper. Cover the pan and cook until the leeks are tender about 10 minutes. While the leeks are cooking, peel the red pepper and remove the core seeds. Cut into narrow lengthwise strips. Add the red pepper to the leeks, raise the heat to medium-high and saute uncovered until the pepper is tender and the leeks have lightly browned, about 10 minutes. Remove the vegetables from the pan and set aside. Add the remaining 2 tablespoons olive oil to the pan and place it over medium-high heat. Put the flour on a plate, evenly coat the fish fillets in it, and shake off any excess. Test the oil in the pan with a drop of flour to see if it sizzles. When the oil is hot enough, add all the fish to the pan and saute until both sides of the fish are lightly browned. Add the white wine, season the fish with salt and pepper, and put the vegetables back in the pan. Lower the heat to medium and cover the pan. Cook until the fish flakes easily when prodded with a fork or spatula, about 5 minutes. Remove the fish from the pan and, if the sauce is too thin, reduce it over high heat until it coats a spoon thickly, and pour it over the fish. Serve at once.