Browsing through the endlessly fascinating tome titled "The Software Catalogue -- Microcomputers" (Elsevier Scientific Pubs., 1,386 pp., $75, quarterly updates $28.95), a bloated volume roughly the dimensions of the Tokyo yellow pages, I was reminded of the old joke about the door-to-door vacuum cleaner salesman who had canvassed all the city neighborhoods and decided to peddle his wares in rural districts.

Early one morning the salesman knocked on the door of a rustic cabin at the end of a dirt road in a secluded mountain hollow. "Is the lady of the house in?" he asked. When she came to the door, he brushed aside all her protests, got out his vacuum, and launched into his demonstration.

"But, but we don't . . . " the lady started to say. The salesman cut her off and went on with the sales pitch: "This machine can do anything! There's no problem it can't solve." Before she could stop him, he was showering dirt on her floor -- talcum powder, egg shells, black mud, chicken feathers, and a nice thick topping of sawdust. The lady tried to interrupt: "But . . . "

"I know what you're thinking, ma'am," the salesman went on. "But there's nothing to fear. Why, if my vacuum won't pick up all that dirt, I'll get down on the floor and eat it."

"Well, I'll get you a fork," the lady said. "I've been trying to tell you. We can't use it. We don't have electricity."

Those of us who are hooked on personal computers don't have that particular problem; we've all got electricity. But we can still feel a twinge of sympathy for the lady of the house when we look through a book like that huge software catalogue.

In a sense, the catalogue amounts to the same sales pitch for computers. "These machines can do anything! There's no problem they can't solve." That's certainly the feeling you get scanning the 10,757 programs listed in the current edition of the Elsevier catalogue.

But like the lady of the house, we can't use it.

The problem is money. Software consumes a lot of it. So much, in fact, that people who aren't descended from a Rockefeller can rarely afford to go out and buy programs the way we buy, say, books or records. Not many people -- or businesses, for that matter -- have the cash to buy a few dozen pieces of software.

Instead, most of us get by with the five or six programs we really need, occasionally coming up with the money to buy a new spelling checker or an alien-blasting game for the kids (well, mainly for the kids).

For we average computer addicts, reading the Elsevier catalogue is nothing more than a voyage to dreamland.

It is intriguing to read this mammoth compilation of programs, which runs from "Aashto" and "Abacus" through "XIOS," "Yi-Ching," and "Zyr." It's fun to speculate about what you would do with a program called "Thunderclock Plus," or to figure out who could use software bearing names like "TLDIS," "AXFRES," "Pow Wow," "Icetrack," or "NewYou."

Clearly, much of the software out there is aimed at a specialized audience. There is evidently a loyal, if limited, market for programs such as "Bowling League Secretary," "Campaign Manager," "Hebrew Scribe," "Track Handicapper," "Dairy Herd Health Manager," "The Ark," (a church-management program), and "OrderIdent," (which identifies all North American insects). But for those of us who aren't running the bowling league this season, there's a limit to how much we want or can afford to depend on software.

This leads to an important consideration for the computer buyer. Is your choice really limited to one of the computers (i.e., IBM, Apple, or the clones thereof) that can run these thousands of programs? Wouldn't you do better to take advantage of a better-priced machine -- a Kaypro, a Zenith Z-100, an Epson QX-10, a Morrow Micro-Decision -- that works nicely but has a smaller software selection?

In many cases, the answer is yes. Get a Kaypro or whatever with its free collection of bundled software and forget the Elsevier catalogue.

Ironically, a choice like that might actually open the door to a larger world of software, because many of the computers with a limited selection of commercial software have a broad and varied collection of free, or "public domain" programs available. How can you get these free programs? Tune in next week, right here, for a roadmap through the public domain.