Call it gadgetry and gimmicks, but Casio Computer Co. Ltd.'s ultra-thin, ultra-cheap products -- including watches, calculators, radios and televisions -- have made it into Japan's fastest growing consumer electronics company.

The key to the 28-year-old company's success is its superb ability to package its proprietary electronics technologies into products that are cleverly designed and priced so low that they become impulse buys.

The Tokyo-based firm plans to churn out nearly 100 million products this year as it seeks to exceed $1 billion in sales. This year alone, it will begin manufacturing 3.5 million pocket calculators a month in addition to its watches and its new line of pocket radios and televisions.

The United States consumes about one-third of Casio's output, and company Chairman Kay Casio said he expects half of all Americans to own products that "carry the Casio name" by the decade's end.

"We are a 'wants gratification company,' " said John MacDonald, president of Casio Inc., the company's U.S. subsidiary, whose revenue has jumped 44 percent from 1983 levels to nearly $350 million last year. "Ask me who needs one of these and I don't know; but ask me who wants one -- now I can answer that."

With more than 1,100 engineers -- their average age is 27 -- Casio has a tremendous technological resource to use in building on its philosophy of finding niche markets that generate high-volume production six to 12 months before the competition can get started.

In 1981, Casio told its technology division to "make a calculator the size and thickness of an American Express card," said Kay Casio.

Two years later, using a thin-film technology and specially designed computer chips, Casio introduced the first calculator that could be slipped into the credit-card window of a wallet. The firm came out with solar-powered versions of the calculator, and now the thin-film product is one of Casio's fastest-selling.

Further exploiting the thin-film approach, Casio has just introduced what it calls "the world's thinnest radio." Priced at $29.95, weighing 0.7 ounces and with a thickness of 1.9 millimeters, the Casio FM card radio was one of the most popular items here at the Winter Consumer Electronics show.

Casio's MacDonald said the card-like quality of the radio makes it a good candidate to be handed out as a premium. "We can manufacture a few thousand and slap an FM radio station's call letters on it as a promotion," he said. Of course, Casio also can command an added profit for those special production runs.

The Casio product that has produced the greatest excitement at the consumer electronics show is the TV-21.

The battery-powered, pocket-sized television set weighs less than 7 ounces and has a 2-inch diagonal screen that uses liquid-crystal technology to display a high-quality black-and-white picture.

Several companies now market hand-held televisions, but Casio is the first to price one below $100 -- and several distributors predict that the model will sell for less than $80 by year's end. Casio also will market a hand-held color television set for less than $300.

One of the fastest-growing and most profitable segments of Casio's business is the company's electronic music group, which was launched in 1980. Last year alone, U.S. sales of the company's electronic keyboards jumped by more than 175 percent.

While generating only 20 percent of Casio's revenue, electronic music sales account for one-third of Casio's profits; watches and calculators each account for one-third of the company's profitability.

In true Japanese business fashion, Casio is more market-share-driven than profit-oriented.

"We gun to be first in market share," said Casio, "and it is very important for us to be the continuous price leader in the field to get to that. If we have dominant market share, profits will follow."

However, Casio said that he is prepared to make acquisitions if his company's existing technology base proves unable to keep up the company's bid to grow at least 25 percent a year. He also is exploring the business market as an avenue for growth. The company has just launched a line of electronic typewriters and may enter the personal-computer market using its liquid-crystal-display technology as a launching point.