There are children in our midst - regular little Leonardos they are too! - who can play a computer until it coughs up the population of Chad, figures the cube root of 7.4362, and sings two choruses of ''The Battle Hymn of the Republic.'' And after that, the junior da Vincis go out to the garage and make elegant refinements to the fuel-injection system on the family car or build their own television set from scratch.
On the other hand, there are adults who can't snap together two pieces of Lego. Overmatched by any equipment more complicated than a push-button phone, we live in fear of phrases like ''Simple to assemble'' and ''Even a child can operate it.''
Well, it's not quite as bad as that. But some of us are hiding in our gardens as Dick Cavett tries to tempt us with another kind of Apple. Techno-mechanical primitives already, we threaten to fall further behind as the world divides itself into software, hardware, and nowhere.
Once we had trouble fixing things. Now we have trouble even working them.
We are the gauche who blush beet-red from ignorance in the presence of our ever-more sophisticated robots. And yet something in us does not reach out to the new knowledge. Why?
Twenty-five years ago we could buy Lancelot Hogben's ''Mathematics for the Million,'' stack it on the bookshelf next to ''War and Peace,'' and feel we were progressing nicely. As long as one could snap light switches on and off with a certain insolent panache, one's self-esteem remained intact as a 20th-century man. Who was to know?
No more. Have you tried to dial a washing machine lately, or just set up a record player? The skill that goes into operating allegedly automatic equipment!
In the Age of the Microchip we techno-mechanical primitives are beginning to stand out like Neanderthals.
How can we overcome our diffidence? How can we keep from regressing even further, like some strange anachronistic tribe, left behind as a curiosity for the space travelers?
It has occurred to us lately that we sci-failures will cross the two-culture bridge only by holding onto our security blanket - language. This, we assume, is one of the premises behind a new book called ''What's What,'' subtitled ''A Visual Glossary of the Physical World'' (Hammond, $30). The authors, David Fisher and Reginald Bragonier Jr., have had the patience to understand that our kind are not necessarily clumsy oafs. It's just that we verbalizers become functionally illiterate with our hands when silence sets in. We need description , commentary to go with our acts, not simply equations. We fumble for words the way the naturals reach for tools or their pocket calculator.
''What's What'' shows, and ever so comfortingly tells. Everything from Little Leonardo's home computer to an oil drilling platform is pictured and broken down into labeled components. The 55 parts that constitute a jet cockpit are pointed at by arrows - with words for them at the other end. No less than 565 pages of whatchamacallits are diagramed thus.
We were charmed by the care taken to identify common objects: the 18 parts of a shoe, including throat, quarter, and lace aglet; the 12 parts of a light bulb, including mica disc, button rod, and stem press; the six parts of a paper bag, including face, bellows, and serrated edge.
How could Adam help loving the creatures once he pronounced their names?
We have not had such an illusion of technical mastery since we read the chapters on whaling in ''Moby Dick'' at the age of 12 and felt competent to ship out as a second mate at least.
''Glory be to God,'' Gerard Manley Hopkins said, for ''all trades, their gear and tackle and trim.''
After identifying the ''anti-skate'' device on our record player, we found the courage to correct a tendency to skid in the ''tone arm.''
Elementary for you. But, for a couple of minutes, we felt like Isaac Newton.