A number of readers have called or written to ask for advice on choosing a "personal word processor" -- a relatively new product that is, in essence, a scaled-down version of the "dedicated" word-processing machines that used to be common in offices.

If you want advice on buying a "personal word processor," you've come to the right place. This column has clear, concise and unequivocal advice on which personal word processor you should buy: None.

To put it as delicately as possible, you'd have to be out of your gourd, stark-raving mad, or at least deeply bewildered, to pay the asking price (generally from $750 to $1,100) for one of these units.

I've looked over some personal word processors. Generally, they consist of an electronic typewriter connected to a monitor and -- sometimes -- to a disk-drive unit. (In some cases, there's a separate keyboard and printer instead of the typewriter). You type a letter, article or whatever on the typewriter, make corrections using the monitor, save your text on the disk drive and then hit a key, and the typewriter automatically types the letter.

This is almost precisely what any personal computer equipped with word-processing software and a printer will do. The "personal word processor," however, can't do anything but write. A computer, in sharp contrast, also can do ten thousand other chores, from filing your taxes to teaching you backgammon to looking up any entry in the Encyclopedia Britannica.

The difference between a personal word processor and a personal computer is the difference between riding the bus and owning a car. The former is a simple way to travel a single, unvarying route; the latter can take you anywhere once you learn to drive.

If these one-dimensional word-processing machines were really cheap -- say, one-fifth the price of a personal computer -- there might be some minute rationale for buying one. But at prices that are very nearly equal to the going price of a computer, a personal word processor seems a crazy investment.

If money is your criterion, you can get the tried and tested Commodore 64 computer -- complete with monitor, disk drive, word-processing software and a reasonably good printer -- at any K mart for $900 or so; that's less than some of the home word-processing machines. For $250 more, you can have a complete Apple II unit; for another $150, you're in the world of the IBM-PC clones. Any of these packages will do all the word processing you want and dozens of helpful tasks far beyond the meager capacity of a "personal word processor."

Why, then, are Smith-Corona and other intelligent firms marketing these word-processing units for the home?

The very existence of the product is testament to the personal computer industry's continuing inability to overcome the deep strain of computerphobia in this land. The personal word processor can't do much, but what it can do it does very, very simply. This clearly has appeal to people who were put off once and for all when they opened a personal computer manual to the first page and were met with a greeting like "Boot up DOS and transfer the system to a formatted diskette in drive B:." There are at least eight words in that sentence that mean nothing to the computer neophyte.

The readers who talk to me about personal word processors are saying, essentially, that they have no great interest in microelectronic design or cybernetic theory; they'd like to send a letter to Mom without first earning a degree in computer science.

This is an understandable and legitimate request. But the personal word processor is an overpriced, underpowered means to fulfill it. It seems to us far wiser to invest in the hours it might take to learn the ropes of a personal computer than to settle for the simplicity of an inflexible machine limited to a single application.

If you need a cheap, easy way to bang out letters, you might look at one of the new electronic typewriters, which can be had for $350 or so with lots of useful features. Once you're in the market for a real word-processing tool, however, forget the "personal word processors" and go all the way -- get yourself a computer.