In the fast-paced computer market, where last year's hot item quickly becomes this year's dinosaur, many people sit anxiously on the sidelines, afraid that if they buy a computer today, they may miss out on a fancier one released tomorrow.

But a growing number of people are taking just the opposite approach: buying inexpensive, used equipment that often does the job as well as a newer model.

The used computer market, almost nonexistent a few years ago, is starting to boom as some computer owners sell their older models to get more sophisticated machines. Others want to get rid of nearly new equipment after deciding that high-tech is not for them.

Washington upholsterer Noah Coates, 28, for example, spent about $1,400 on a brand new Apple IIC portable computer, monitor and two programs this fall, then turned around a month later and sold the entire package for $950 after he had second thoughts about putting that much money into a computer. His experience is not unusual.

Buying used equipment "is a great way to get your feet wet without spending very much money," says Dona Z. Meilach, author of a series of computer buying guides, including an upcoming book, Before You Buy a Used Computer (Crown Publishers).

Meilach estimates that secondhand buyers can often save anywhere from 25 to 60 percent of the cost of new equipment and "get a lot of software tossed in to sweeten the deal."

But she and other experts concede that buying used can be a risky venture for people who don't know that much about computers or how much a piece of equipment is actually worth. The cost of new computers has dropped so quickly in the last several years that a new model could be as cheap as some earlier versions advertised through the classifieds.

"Someone might have paid $2,000 for a computer. He wants to get as much money for it as possible, so he tries to sell it for $1,000. But the same thing new today might sell for $1,000," cautions Meilach. "So you shouldn't pay more than $500 for it used."

She urges potential buyers to do their homework first and check the list prices of new equipment before buying anything used. Other experts urge first-time buyers to ignore the used market altogether.

"If it's your second, third, or fifth computer, there's nothing wrong with buying used if you can get a big enough discount to justify paying for repairs if something breaks. But I would not recommend buying used for the first-time buyer," says Brooke McCauley, president of Peoples Computer, an Arlington store which deals in both new and used equipment.

Most experts claim that computer malfunctions are rare after an initial break-in period. True, says McCauley, but adds: "Computers do break down -- not as often as a car does, but when they do, they're expensive to repair. A typical repair costs $200 to $250 for a machine that you may have only paid $800 for if you have to replace a part."

And, he adds, mechanical units like printers, disk drives and keyboards wear out with use. But in McCauley's view, one of the biggest problems in buying used equipment, especially from a private party, is that novices are often left without the technical support or warranties they may get from a dealer.

Computer novices also have to be careful not to buy an obsolete model for which there is no service contract, says attorney Daniel T. Brooks, 43, of Springfield. Brooks, who has bought five used computers for his home-based legal practice, says he insures himself against future trouble through the same kind of service contracts people buy for their washing machines.

Why does he prefer used computers? "That's easy," he says. "Money."

Brooks bought his first in 1981, after deciding that he needed a word processor, a high-priced computer designed specifically for editorial work. Instead of spending more than $15,000 for a new one, he paid $3,000 for a Lexitron nearly 10 years old. Last year he bought a second one for $300 and spent another $1,000 to upgrade it.

Such easy-to-use secondhand word processors may be a much better buy than a new personal computer for lawyers, writers and other professionals who want to use the equipment solely for editorial work, says Tim Rizer, owner of Item, Inc., an Annandale company which deals in used equipment. "The key is to get the right piece for the right circumstances."

"A lot of people don't realize there's a market for used machines," says Paul A. LaZar, president of Generation 5, a Silver Spring company which buys and sells used computer equipment.

Those who do are often nervous about buying someone else's discard. "People are scared," says LaZar. "We are conditioned to think new and improved. But more is not always better."

Joel Makower, 32, a Washington writer, editor and president of Tilden Press, a book-packaging firm, found that out the hard way. He made the classic computer mistake: overbuying.

"I wanted good equipment," he says, and consequently spent $2,300 on a new letter-quality printer. He soon discovered, however, that the equipment, which prints only 35 characters a second, was far too slow to handle his large volume of manuscripts. A year later, he ran a classified ad and sold the printer for $2,000. He then purchased two new less expensive models: one fast printer for manuscripts, and a slower letter-quality model for business correspondence.

One of the greatest advantages of the growing used computer market, says writer Meilach, is that people like Makower no longer have to feel stuck with an expensive mistake. "If you don't like it or want something else, you can turn around and sell it."