They say that apes with typewriters and plenty of time could eventually reproduce the works of Shakespeare. By the same token, a flock of moths might come up with a five-year business plan on Hewlett-Packard Co.'s new entry in the microcomputer sweepstakes, the HP 150. What gives the moths their business ability is the 150's novel "touch sensitive" screen, which allows the computer to perform its magic at the brush of a finger -- or a wing.

For the desktop market, it is a bold innovation, aimed squarely (if belatedly) at the IBM Personal Computer, the PC clones, and Apple Computer Inc.'s Lisa. If the competition proves to be as sensitive as the 150's screen, the microcomputer business itself is apt to get a bit touchy over the next few months.

Hewlett-Packard, for its part, figures that it is now at least a year ahead of the competition, having spent 15 months developing the 150. Although the computer's internal code name is "Magic Touch," the technology does not, in fact, rely on physical contact. Instead, the video display is surrounded by light-emitting diodes that produce an electronic grid in front of the screen -- rather like the invisible beam's guarding the Hope diamond. The machine responds at the point where the grid is broken.

The system runs software based on icons or pictures -- as Lisa does, except that it does not need a "mouse." Backgrounds of graphs, for example, can be painted by "dipping" a finger (or a pencil) into the selected pattern. Or a database can be sorted and searched via a finger-operated, on-screen menu. One HP database management program produces the image of a Rolodex card file on the screen, accurate down to the little slots at the bottom. "Turn" one "knob," and the cards flip quickly. When you find the name you want, you simply point, and the entire record appears. So far, the keyboard has been gathering dust.

Third-party software writers have been quick to follow the finger. Touch-screen versions of such popular software as VisiCalc and WordStar are already available, and more than 30 other programs are currently being adapted for the 150, including the hot-selling Lotus 1-2-3. The system also operates under MS-DOS 2.0, so that you can use many existing programs (although without touch sensitivity). Then again, if you are looking for inspiration, or just feel like doodling, the 150 draws nifty patterns around points randomly touched on the screen.

As much fun as it is, the basic system, with two disk drives, will sell for only $4,000 or so -- roughly comparable to the cost of an IBM PC, and about half the price of Lisa. Moreover, the 150 comes with 256 kilobytes of random access memory (expandable to 640), has three data communication ports, and can link up with IBM and HP mainframes and minis.

But, Hewlett-Packard plans to gear its marketing not so much to the power of the computer (it incorporates an Intel 8088 16-bit chip) as to its size and convenience. Indeed, an entire system, including an optional thermal printer built into the video display box, takes up only 1.7 square feet of desk space -- about as much as an in-basket. To pull this off, HP has gone to 3 1/2-inch diskettes -- "stiffies" -- in place of of the 5 1/2-inch floppies used by most other micros. In addition, the 150 has a 9-inch, high-resolution screen, rather than the popular 12-inch monitor.

HP's pitch will be that the 150 can fit onto the corner of any desk, eliminating the need to acquire additional furniture to house the microcomputer system. Of course, the pitch could backfire if the average executive perceives "small" to be "less." If it works, however, once-serene IBM may find that it faces some strong competition in the small business marketplace, after all.