A college buddy of mine who made good in Hollywood was once hired to direct the third installment in a well-known series of fluffy slapstick comedies. The previous movie had tanked at the box office, and my friend said the producers gave him a single marching order: ''Save the franchise.'' That beautifully crass dictum kept floating through my brain as I watched Wayne's World 2 (PG-13) and Sister Act 2: Back in the Habit (PG). Follow-ups to breezy sleeper smashes, each shows the strain of giving the audience the same thing but different that turns whimsy into clammy business. Amazingly, both of these franchises turn out to be going concerns.
Consider how wifty Wayne's World was to start with -- a genial tangle of catchphrases and attitude that hit it lucky. That was fifteen cultural minutes ago, and the sequel has to fight uphill to even matter. Wayne's World 2 hitches its wagon to the pop-parody style of the Naked Gun films, rather than to WW's slacker bonhomie. As Wayne (Mike Myers) and Garth (Dana Carvey) struggle to put on a giant concert, the movie ricochets from one movie spoof to another, tossing in random star cameos along the way (I especially liked Kevin Pollack as a ''partial ocular albino'').
But if the filmmakers have sacrificed some of the mischievous stoner charm, they actually deliver a higher hit-to-miss gag ratio. For every dead end, like the subplot about a temptress (Kim Basinger) seducing Garth, there's a delight, like a Village People number that seems to erupt out of nowhere. Best of all is a kung fu scene that so nails the threadbare particulars of the genre -- the cruddy dubbing, the gnashing sound effects, actor James Hong -- that it briefly reaches a higher, more original lunacy. It also made me laugh harder than anything I've seen at the movies this year.
Conversely, Sister Act 2 doesn't have one original idea in its entire 100 minutes. Somewhat bizarrely, it doesn't matter. The plot isn't just a retread, it's bald: You can practically hear the filmmakers arguing over how to get Whoopi back into that wimple. Her fellow nuns are now running a decrepit urban parochial school, but their teenage pupils are so hard-boiled that Deloris Van Cartier -- a.k.a. Sister Mary Clarence -- is called in to whip them into shape as a choir. That's right: It's Mickey Rooney and Judy Garland putting on a show by way of To Sir With Love. The recycling's so cheerily blatant it almost short- circuits criticism.
What saves the movie is a young cast with astonishing talent and energy: You respond to their high spirits more than to the hackneyed characters they play. It helps, too, that the Motown parodies of Sister Act are largely traded in for modern pop-gospel. The scene in which the fierce, lovely Lauryn Hill sings a few shivery bars of ''His Eye Is on the Sparrow'' feels like the first genuinely religious moment in the series.
With all that, Sister Act 2 is pretty much a mess. It takes forever to get on its feet and doesn't make a lot of sense once it does (James Coburn has been cast as a bad guy, but he doesn't do anything bad -- he just stands around and glowers). Still, Goldberg seems more relaxed this time, and the central troika of nuns, played by Kathy Najimy (bubbly, daft), Mary Wickes (old, grumpy), and Wendy Makkena (sweet, naive), remains fun. Anyway, how can you hate a movie that gives Kathy Najimy second billing? And so what if the story rips off Mickey and Judy? Somewhere, in his rococo heaven, their old boss Louis B. Mayer is smiling: His franchise has been saved too. Wayne's World 2: B; Sister Act 2: B-