"Gizmo," now at the Key, is a lighthearted, casually amusing novelty film, a documentary intended to recall and salute obscure inventors and daredavils, particularly those whose inventions and stunts met with failure.

Though not an unrelieved catalog of failure, this compilation relies on a great deal of newsreel footage recording the calamitous demonstration of some ingenious mechanical device, frequently a homemade flying machine.

Even the successful feats tend to be daffy and disarming. For example, daredavil Tilly Schein whizzes across Time Square hanging by her teeth from a high wire. Human flies scale the facades of office buidlings. A strongman exposes his iron gut to a variety of turtures. One exceedingly curious specialist inflates a balloon through his ear.

the ideas, according to producer Howard Smith, who stopped in Washington briefly to promote the opening, was an effectionate tribute to people creative, courageous or foolhardy enough to try anything once. It might mean inventing and testing a gizmo, or it might mean turning their own bodies into experimental gizmos. The complsion to bottom through on their crucial element was the willingness or brainstorms.

"The more I travel, the more patriotic I get," said Smith, who maintains an ongoing journalistic identity as the "Scenes" columnist on The Village Voice and broke into movies as the coproducer-director of "Marjoe," which won him an Academy Award for best feature documentary.

"When you're at home, it's natural to complain that nothing work right, that the government doesn't know what the hell it's doing, that Americans are too materialistic. You begin to change your tune when you encounter societies that are really stagnating bureaucracies that are totally unresponsive and money-grubbing foreigners who act as if Americans were created to be swindled.

"I've come to believe that there is a unique sort of openness about Americans. It's one of the things foreigners like about us, assuming they're disposed to give us the benefit of the doubt to begin with. It's a willingness to try things, even if it means falling flat on your face and looking like a terrible fool.

"I wanted the film to capture that spirit, which is essential to any creative endeavor. All successful innovations are built on countless failed attempts. I've tried to structure the material so that audiences who begin laughing at these people will end up laughing with them."

I'm not sure Smith achieved the modulation he had in mind. "Gizmo" is an entertaining miscellany, but it doesn't evolve or deepen, as it goes along, so much as merly terminate on an explicit inspirational note, with shots of hang-gliding and the statement that if man's reach doesn't exceed his grasp, what's a heaven for?

Although the running time is only 79 minutes, the movie maintains such a consistent level of gently mocking humor that I began to weary of it and wish for clips that broke the pleasant montony by hitting some unpredictable highs and lows.

There's a minimum of imformation about the intrepid pioneers Smith and his assistants dredged up from the newsreel libraries of the world. According to Smith, an early version had volunteered considerable background data, but he began eliminating the commentary drastically when he found that preview audiences seemed to resent it, preferring the abstract comic effect that results from a succession of unidentified zanies in action.

Smith also revealed that he decided to abandon an earlier working title, "Eureka!," when he discovered that the term seemed to be a complete mystery to many previewers. "I was a little astonished at that," Smith said. "I took it for granted that everybody learned about Archimedes shouting 'Eureka!' in school or by watching quiz shows or something. You just pick it up, right? Not anymore, it seems.

A lot of people who worked on the film were crazy about 'Eureka!,' so the switch provoked a little bitterness. But I didn't see any alternative, and 'Gizmo' agrees with outsider. It'll cause us fewer problems in foreign release also. We won't have to translate it. 'Gizmo' sounds catchy and American even in places where they don't know what a gizmo is."