A movie with a title like "Airplane II: The Sequel" enjoys a built-in defense mechanism against criticism: You can't accuse it of being derivative without looking ridiculous. So let's put it this way: While "Airplane II," proves to be a breezy and tolerably consistent follow-up to its successful prototype, a parodistic copy that relied less on jokes from the original might have seemed a shade fresher.

The writing-directing team responsible for "Airplane!" took the extraordinary step of sending out a press release disclaiming any responsibility for "The Sequel," a ludicrous exercise in show-biz vanity, since the new picture is certainly the sincerest form of flattery. Moreover, it's not as if "Airplane!," deliberately and sometimes irresistibly funny as it was, surpassed many of the pictures it was kidding, especially "Airport '75" and the sublimely stupefying "Airport 1979: The Concorde," for sheer hilarity. It's funny how one big hit can distort the old sense of proportion.

"The Sequel" makes a half-hearted attempt to take a fresh approach by projecting the premise of mid-flight peril into the immediate future. Mayflower One, the first passenger shuttle to the moon, blasts off from Houston with a mad bomber on board, but a defective wiring system and a tyrannical computer jeopardize the trip even earlier, sending the ship on a computer-controlled path toward the sun. Several survivors (and an occasional victim) from the "Airplane!" misadventure are reunited, notably the estranged lovers Ted Stryker and Elaine Dickinson (Robert Hays and Julie Hagerty), who've had another falling out so that they can reconcile again through the grace of crisis situation cliche'.

Although Elaine looks no older a generation later, she has new duties on Mayflower One, moving up from stewardess to computer systems officer. Ted, a shuttle test pilot, has been cashiered into a loony bin by a conspiracy of crooked contractors and administrators because of his insistence that the ship remains unsafe. He escapes and catches the flight (there's a good bit connected with his purchase of a shuttle reservation from an "agent" played by Clint Smith) in time to be handy when the crew (old hand Peter Graves as the pederastic Capt. Oveur, plus new hands Kent McCord as a copilot named Unger and James A. Watson Jr. as a navigator named Dunne, accommodating a chorus or two of Oveur-Unger-Dunne puns) is snuffed out by the renegade computer. With the invaluable advice of Lloyd Bridges from Houston (a brilliant reprise of his delightfully frazzled, crusty ground controller McCrosky) and William Shatner from the moon base, utter disaster is once again narrowly averted.

As before, the comic strategy is one gratuitous gag after another, and what prevents it from becoming unbearably gratuitous is the deadpan verve and cleverness of the cast members. They're a more phenomenal comedy troupe than I realized, so imaginative at the bits of character shtick entrusted to them that they seem to get funnier with repetition. Hagerty, for example, plays naivete with a breathy delicacy that makes her Elaine seem a caricature touched with genius, and Stucker has certainly created a prissy persona that gives him an indisputable claim on the Hall of Fame associated with Franklin Pangborn, Edward Everett Horton and Paul Lynde.

Shatner inherits the assignment Stack had in the original film, and he's in wonderful batty-authoritative form. The moon location also seems to inspire such a terrific initial outburst of gags from writer-director Ken Finkleman that you wonder if the whole project might have found a fresh source of humor if liberated faster from the "Airplane!" format and refurbished for science-fiction effects. The hit-and-miss quality of the gags may be suggested by two early swipes at other movies: there's an "E.T." joke that falls flat and a "Rocky" joke that rings the bell.

The duds and bell-ringers keep coming in rapid succession for the next 80 minutes or so, but it's hard to reject a throwaway farce that scores at least half the time, particularly with comic marksmen as attractive as the gang that's been reunited and augmented for this painless trifle.