1. Stack lettuce leaves and cut into thin shreds.
2. In a 3-quart saucepan gently simmer lettuce, broth, and green tea, covered, 40 minutes.
3. In a blender purée soup in 2 batches with margerine, green tea leaves, and sea salt and black pepper to taste until smooth. transferring as blended to another saucepan.
4. Heat soup over moderately high heat until hot.