Dissolve gelatin in water.
Add pineapple and refrigerate until slightly thickened.
Fold in oranges and marshmallows.
Pour into an 8 x 8 x 2-inch pan and refrigerate until firm.
Combine sour cream and mayonnaise, mixing well.
Spread over top of gelatin.
Cut in squares and serve on lettuce leaves.
Makes 6 to 8 servings.