You've looked around, decided it would be fun to have a personal computer at home to experiment with. But you're put off by the expense of bigger units and convinced one of the smaller -- and cheaper -- ones wouldn't be a fair test.

What do you do?

Simple. Consider buying a used home computer.

You can get a good buy on certain kinds of medium-priced, moderately powerful brands, provided you do a little pricing homework on new models ahead of time.

Moreover, along with your machine you'll probably get a lot of software (things like games and home finance packages) that is generally quite costly when purchased new.

And chances are, you'll be able to sell your used machine with reasonable ease if you decide you want out -- or if you want to move up to a more powerful and versatile personal computer.

Recently, I called six individuals who were trying to sell their home computers in The Post classified section to find out why they were selling and what they'd learned from having one.

Half were selling because they wanted to spend the money on other things. Two of them had decided they didn't need a computer in the home, while the third vowed that, as soon as he had more bread, he'd buy another.

The remaining three were selling because they wanted to move up to larger, more powerful computers. (All three of these, incidentally, said their first home computer had been bought used, that they'd owned them for a year or more without problems, and they were convinced that buying a used computer first was the best way to start.)

"Used computers are a good deal," said one Prince William County resident, a computer analyst for General Electric who was selling a version of the Radio Shack TRS-80. "Computers don't really wear out," he said. "They're electro-mechanical, so, as long as you don't move them around, they won't get damaged."

Kenny Lusby, a 16-year-old Oakton High student who is selling a TRS-80 so he can buy an Atari, was equally enthusiastic about buying used equipment. "I got it much cheaper than if I'd bought it new," he said. "And I never had any problem with it."

The reason all of them gave for moving up was that they wanted more power -- more memory, essentially -- in their machines so they could either play more sophisticated games or do word processing. Perhaps coincidentally, all were selling various versions of the TRS-80 and opting for an Apple or Atari computer.

The reasons given by the three who were getting out of the home computer field differed markedly, however.

"I'm just not using it," said Steve Irish, a computer programmer who was selling a TRS-80 III. "Part of the problem, too, is I program all day long anyway."

Chantilly High student Scott Keating said he was selling his TRS-80 I because he wanted to do more, "but I didn't have enough money for a printer. To do word processing, it costs a lot of money. Disc drives, for instance, can get into the hundreds of dollars."

But Jim Wolfe, an assistant manager at a Roy Rogers restaurant who said he was selling in part because he needed a new car, said, "I'll buy another computer in a couple of years when the prices come down and they're more powerful."

Used equipment is generally sound, though it pays to check it out before you leave with it, say those who know. If you are going to experience problems at all, it will more likely be with "peripherals", like disc drives and tape decks (they extract information stored on magnetic discs and tape and then stuff it into the computer's memory so you can use it as well as extract it from the computer to save). They are far more conventionally mechanical than the computer itself, so they're more susceptible to breakdowns from heavy use.

Check them out carefully. Make sure they do what their supposed to do.

"I'm really glad I got mine used," said one Northern Virginian, who had just bought a new Apple II Plus and was now selling his TRS-80 model I. "It was a good introduction to home computing. Didn't cost much and we learned a lot. We knew exactly what we wanted (in a home computer) after that."