Let ice cream stand at room temperature 30 to 45 minutes to soften.
Meanwhile, in small bowl, mix cracker crumbs and butter; reserve 2 to 3 tablespoons crumb mixture. In ungreased 8- or 9-inch square pan, press remaining crumb mixture firmly and evenly over bottom.
In large bowl, beat remaining ingredients with wire whisk until well blended. Stir in ice cream with spoon. Spread over crumb mixture in pan. Sprinkle reserved crumb mixture over top.
Freeze uncovered at least 4 hours or until top of pumpkin mixture is firm, then cover and return to freezer. Let stand at room temperature 15 to 20 minutes before cutting.