Chances are you already have a calculator, an appointment calendar and an address book. The electronics industry would like to sell you a replacement for all three.

Starting at about $25 and topping $500, chip-driven organizers can do the job of virtually any piece of paper or machinery in your briefcase: They can tell time, calculate interest, remind you to pay the bills, keep sensitive telephone numbers secret and ring a bell on the children's birthdays.At their most modest, electronic organizers are nothing more than computerized telephone books that hold a few hundred names and numbers. Some of them can dial a telephone, a handy function for the tender-fingered traveler with plenty of business calls to make. Organizers with dialers sell for as little as $15.

As features and memory increase, so does the price.

The Casio SF-3000 accepts memos, schedules and calendar listings as well as telephone numbers. The average person would find it difficult to exhaust the 3000's 18k memory. But a person who travels extensively on business might prefer the Casio SF-4000, which for $149.99 buys you considerably more electronic storage space. Its 32k memory holds roughly 1,500 numbers and as many memos.

Sharp's Wizard has the same amount of memory, but at twice the price it allows you to transfer stored information to a personal computer. The Wizard capitalizes on the biggest shortcoming in other electronic organizers: Information entered into a less-expensive model is stuck there. There is no way to transfer the day's notes electronically to a computer when you get home.

Do you need a beeping, blinking, key-studded address book with adjustable lighting, a six-line screen and graphic capabilities? Not if you have to ask, computer experts say.

"Right now, they don't do anything that you can't do another way," said Ted Drude, associate editor of Computer Shopper, a Titusville, Fla., magazine for computer users. "It's more of an executive toy."

Electronic organizers can be quite useful, Drude said, but most consumers should consider them something novel rather than necessary.

"There's hardly anything that can be done with that," he said, "that can't be done with a good paper organizer that you carry with you."

Robert B. Miller, vice president of merchandising at Radio Shack's headquarters in Fort Worth, Texas, agrees that the fascination with electronics is the reason for the product's popularity.

"It's a handy device for some people who really need to carry data around with them," he said. "For lots of others it's a gimmick. People like high technology."

Electronic gimmickry wasn't always a best seller. Computer organizers have been around for years, Miller said, but until people got used to computers the organizers got little attention.

"This year they really took off," he said.

High-end organizers drew attention to the less-expensive models, fueling the entire industry, Miller said.

Limited shipments of new Wizards sell "almost overnight," said Joan Hartley, the store's group merchandise manager. "There's usually a waiting list for them."

As gadgets, however, organizers can be fairly expensive. The Wizard sells for $279 to $299, but extra programming cards can inflate that price by $100 at a time. A dictionary-thesaurus card, for example, costs $129.99. The eight-language translator costs $99.99.

As the Wizard's price bumps into that of a lap-top computer, it begins to draw criticism.

Drude at Computer Shopper said customers who need all the functions of the Wizard should consider the slightly larger lap-top computer.

"It's easily small enough to fit in any attache case," he said, and "it gives you much more power than those will ever do." Lap-tops also run software, something hand-held computers are not yet capable of, though plans are in the works.

In the meantime, the Wizard is considered by many in the computer industry to be a niche product with a fairly narrow niche: It's for the person who has a desk-top computer but doesn't plan to buy a lap-top.

If that niche is a narrow one, customers don't seem to know it. Sharp Electronics Corp. will not disclose exact figures, but Gilbert DeLiso, a national marketing manager, said sales are in the tens of thousands, ahead of the company's expectations. Customers are "constantly clamoring" for more of the $100-plus cards that expand the Wizard's capacity, he said.

"People will pay for the convenience of size," he said, "even though the total cost of putting one of these things together may be several hundred dollars."

Hughes said customers don't hesitate to buy Wizards, but a few bring them back after trying to decipher the 200-page instruction manual.

"If it's something people are interested in, I don't think the price is a major factor," she said.

Despite the inch-thick instruction manual, the Wizard is not difficult to use, Hughes said. Symbols on the Wizard's keys show the user how to find certain functions. To call up telephone numbers, for example, push the button with a picture of a telephone.

Electronic organizers look like calculators in a fancy jacket, but the electronics industry is hoping fervently that they will never be as inexpensive.

"Within 10 years a calculator went from over $100 to $10, performing the same functions," said Andrew Gaffney, associate editor at "This Week in Consumer Electronics," a trade publication in New York.

Partly to delay such a fall in prices, the industry puts high-end products in the spotlight, he said, and markets them to professionals.

But Miller at Radio Shack calls that wishful thinking. Without predicting a date, he expects electronic organizers to become as inexpensive and commonplace as calculators.

"They'll be cheap. They'll be dirt cheap," he said. "I'm not saying a $79 product today will be $4, but it might be $25.

"Everyone will have one. They may never use it, but yes, everyone will have one."