Despite his British reserve, Clive Sinclair would probably recoil at the thought that he's become the Henry Ford of personal computers. Yet the parallel between his machine and the Model T are irresistible: It's cheap (under $100), functional, bizarrely elegant and it comes in any color you want as long as it's black.

In fact, the Timex-Sinclair ZX81's price and functionality have literally redefined the personal computer marketplace. Ordinary consumers can now afford to wonder what a computer can do for them and Sinclair's competitors are forced to justify the higher prices for their machines. Sinclair's ability to low-ball the price while keeping most of a computer's versatility has--along with Timex's marketing clout -- given it a dominant market presence in America in less than a year. Over 700,000 units of ZX81 and its predecessor ZX80 have been sold worldwide in the past two years, making Sinclair's company -- Sinclair Research -- claim that it is the largest volume personal computer manufacturer in the world. And, says Sinclair, there is yet another generation of low-cost and more powerful Sinclair computers to come.

With his high forehead, thinning hair and thick glasses, Clive Sinclair looks precisely what the British call a boffin -- an academic grind. Yet Sinclair never attended college, and worked as a technical journalist before launching, at the age of 22, the first of a series of entrepreneurial ventures in consumer electronics in the early 1960s. fter some messy financial mishaps, Sinclair left his old company to form Sinclair Research in 1979. The company's first product -- the ZX80 computer -- offered in 1980 and marketed through mail-order, did phenomenally well. A year later, the new and improved ZX81 was being produced at the rate of 60,000 units a month. Yet the ZX81 was sold even cheaper than the ZX80.

"The ZX81 was a better machine -- more powerful, more elegant -- but we priced it less and everyone said we were crazy," said Sinclair. "But we go by cost-led pricing. There are two reasons for this: first is that there is a relationship between selling price and sales volume; that curve has a peak and we can show that the peak happens at a small profit margin. So, counter intuitively, the low price gives us the highest profit. The second reason is that our pricing deters competition. We know that in our case some of the Japanese companies have canceled their personal computer plans because of us."

Overnight, the ZX81's success in England spawned a host of cottage industries designed to produce both hardware and software for it. Indeed, several "Sinclair Faires" were held to celebrate the machine, its growing community of users and its creator -- "Uncle Clive," as he is known. But Sinclair Research was not satisfied with the ZX81 as the staple of its product line. The company introduced a next-generation machine in England in April this year -- the Spectrum. "It's always a complicated juggle between price and performance," says Sinclair. "We want to have a product that is broadly better than the competition so we look at all the competitors, we get their machines and we try to position ourselves so that nobody can take our machine and say, 'Ah, but it doesn't do this . . . ' "

The Spectrum currently is available only in England, for 125 pounds ($215), and represents a huge technological leap over the ZX81. It offers eight-color graphics capability along with such Sinclair-designed peripherals as micro-floppy disc drive and communications modems. Also, the Spectrum's keyboard more nearly resembles a typewriter keyboard.

Yet this innovation puts pressure on Sinclair's American partner, Timex, which has marketed Sinclair Research's computer products in the United States since August. The Spectrum could induce consumers not to purchase the Timex-Sinclair ZX81 and wait instead for the Spectrum.

Yet another more serious problem for Sinclair is the very cottage industry that helps support his machines. That industry actually competes with Sinclair products by producing rival hardware and software. Since Sinclair Research is not really a software house but rather a hardware innovator, says Sinclair, it has had to "scout out good software, buy it or publish it." Timex is marketing Sinclair software in the United States and is reportedly talking with several video game design companies to provide game software for the machine.

However, computers aren't the only market weapon in Sinclair Research's corporate arsenal. Early next year, the company plans to introduce the Microvision TV--a tiny quarter-inch-thick hand-held flat-screen TV measuring 4 inches by 2 inches to sell for less than $100. "It's quite a device," Sinclair smiled. It is expected to add a great deal to Sinclair's revenues--currently estimated at 27 million pounds (about $46 million) per year.

Yet even the Microvision should fold back into the computer. It's purely a logical step, Sinclair allowed, to package computers and Microvision into a single powerful unit that makes a computer and display device both portable and -- in keeping with Sinclair's marketing principles -- cheap. "The machine we're developing for the end of next year or the beginning of 1984," says Sinclair, "will merge those two technologies."

But it is important to remember that Sinclair Research isn't just a computer company but a consumer electronics company. One of Sinclair Research's products-to-be bears no resemblance at all to its past innovations. In fact, it makes the Clive Sinclair/Henry Ford comparison quite legitimate. Come 1984, Sinclair expects to market a consumer electronics product with wheels -- an electric car. He declined to reveal details but he promises to unveil it not at the national automobile show but at a consumer electronics show CAPTION: Picture 1, Clive Sinclair, 41, the brains behind the ZX81, the world's first true mini-copmuter priced under $100; Picture 2, More advanced typewriter-like keyboard of Sinclair's next-generation "Spectrum" minicomputer.