How you feel about The Magical Legend of the Leprechauns (Sunday, November 7, 9 to 11 p.m. and Monday, November 8, 8 to 10 P.M.; NBC) will depend entirely on the state of your whimsy. My own whimsy has suffered some from recent Senate votes on campaign-finance reform and the nuclear-test-ban treaty, so I had a hard time sitting still for a love affair between a visiting businessman (Randy Quaid, who wants to buy up rural Ireland for vacationing Americans) and a skinny-dipping Irish wench (Orla Brady, who would have stopped Julius Caesar in his tracks) in the middle of an all-out war (a sort of West Side Story in short pants) between the Leprechauns and the Fairies. Whoopi Goldberg has her moments as the Grand Banshee who lives in a room-service Ritz; Colm Meaney and Roger Daltrey work hard as Little People with or without wings; and the special effects can be counted on to go Poof, the Magic Dragon. On the other hand, as in a public-TV pledge week, there is altogether too much step dancing.