You thought the computer was the big expense. But before you got out of the store you'd spent hundreds more for those deceptively thin -- but expensive -- floppy disks of software.

Word processing, spreadsheets, databases, packages to plan your money and pay your taxes, programs to teach your daughter math and games to keep your son entertained. By the time the salesman added up the bill, the software came to (gulp) more than the hardware. And there was still the learn-to-type program and the French lessons . . .

But now -- at least according to some sources -- you may not have to buy another piece of software. Bucks County, Pa., high-tech writer/consultant Alfred Glossbrenner calls the existence of thousands of free -- or nearly free -- public-domain programs among "the best-kept secrets in the microworld." He has gone public with the secret in his book, How to Get Free Software (St. Martin's Press). There are hundreds -- even thousands -- of free programs for every machine, many equal to, he claims, or better than their commercial counterparts.

"Free software does everything except the dishes," says Sheryl Nutting, president of American Software Publishing Co., a Washington, D.C., firm that has compiled, catalogued and now distributes more than 10,000 public-domain programs.

There are games such as the absorbing and complex Adventure, in which you're a treasure hunter in an endless maze of caverns; complete business packages like Bizmaster, which automate your accounting system, payroll and mailing lists; educational software from counting to calculus.

Among the best of the freebies are communications programs, such as the classic Modem 7 and the newer MEX, that enable your computer to talk with other computers. And if you've ever sworn that you would pay any price to be able to recover that file of tax information you zapped inadvertently, you'll be glad to know that there are utility programs such as Unerase, which will do just that -- and for free.

Glossbrenner found free software in hundreds of local users groups, "super groups" that serve as public-domain software libraries of record, commercial software libraries and on-line bulletin boards and electronic utilities such as The Source and CompuServe, from which you can "download" or electronically transfer software to your computer.

The task of turning up free software in the Washington area may involve no more than contacting one of the dozens of active user groups -- nonprofit, largely volunteer organizations -- that have sprung up to provide support for virtually every machine or operating system. Their extensive collections of public-domain programs are distributed at meetings, through the mail and via their own on-line bulletin boards.

But why would anyone invest their time in writing a program and then just give it away?

Free or public-domain software came on the scene when the personal computer industry was in its infancy. Hackers began tinkering with early and imperfect CP/M-based systems, fixing bugs and solving some of the inadequacies of the operating system.

"There was a sense of altruism," explains Texan Greg Platt, PeopleTalk president and co-author of The Free Software Handbook, a collection of the best free CP/M software. "Someone helped me out, I'll help them out."

Hobbyists began experimenting with their equipment, sharing solutions with each other and donating their programs to newly forming user groups. "For many, it's their way of bragging," says Nutting. "They're saying, 'look what I can make this machine do.' "

"It's their tour de force," says Glossbrenner. "It's like Baryshnikov doing an extra pirouette."

For others the reasons are more political -- a conscious rebellion against the high price of commercial software -- and for some, the incentive is profit.

As the micro industry matured, so did the free software movement. The DOS operating system, adopted by IBM, solved many of the problems inherent in CP/M machines. The IBM-PC came to symbolize the serious user, and so it was perhaps inevitable that the "free" software associated with that system should also take on a more business-like veneer. The concept of Freeware, Shareware or "user-supported" software was born.

Freeware was invented by Andrew Fluegelman, San Francisco Bay-area author of the communications program PC-Talk III. His idea was to distribute his software in copyable form through alternative sources -- bulletin boards, and user groups. Take it home and use it, he said, and if you find it useful send me a contribution ($35 suggested). If you don't find it worthwhile, there's no fee.

Bob Wallace, Seattle, Wash., the author of PC-Write, a word-processing program, took the Freeware concept a step further with Shareware. Again, he makes his program available for free, but if you try it and like it, you are asked to send a registration fee instead of a donation ($75), which entitles you to make copies of PC-Write and share it with friends.

If any of these people decide to register their copy, Wallace will rebate $25 per copy. Enthusiastic users can therefore more than recoup the cost of the program, while generating handsome income for the author.

Although the concept has taken root in other areas, it has remained, for the most part, planted firmly in the IBM world. Buttonware, for example, refers to the four IBM programs (PC-File, PC-Calc, PC-Graph and PC-Dial) created by Jim Button, Bellevue, Wash. All sell for under $50 and so successful is this venture that Buttonware is now a million-dollar-a-year business.

It is not surprising that professionally written user-supported programs are among the most popular offerings available through the Capital PC Users Group.

"The trend among new users," observes Rich Schinnell, Rockville, the group's public-domain software libarian, "is that they try the free or user-supported programs before they go out and buy commercial software. Then they might graduate to bigger programs like Symphony or Lotus all-in-one multifunction software packages , but they get their feet wet with the free stuff first. Many never get any further. It suits all their needs.

"A good majority is fully supported well-documented and the cost is about 10 percent of its commercial counterparts."

While feeding your computer entirely on good-quality free or user-supported software may be a reality in the IBM-DOS world, it is less so for some other machines.

"It's not entirely possible in the CP/M world," says Platt who screened more than 1,000 CP/M-based programs but was unable to come up with a word-processing program worthy of inclusion in his top 70.

The sheer volume of public-domain software creates its own problems: that of separating the chaff from the wheat. And once you've located the wheat, what you encounter in some instances -- especially the older public-domain programs -- is poor or nonexistent documentation.

Although Sheryl Nutting acknowledges the problems inherent in the public-domain software, she views them as potential virtues. "A program someone else has labeled useless may be just what you need, and often the bugs may be easily fixed." Some of the fun of public-domain software, she contends, is "taking someone else's contribution and making it better."

One of the arguments against free or user-supported software is that there's nowhere to turn for support. "The support system is just different," claims Glossbrenner. "Instead of going to your dealer for support, you go to the user community."

Indeed, many of the user groups in the Washington area have as their raison d'e tre the distribution and support of public-domain software. On-line bulletin boards are another source of support. "Leave a message on a bulletin board," says Glossbrenner, "and you'll get help from all over the country."

Many authors put their phone numbers on their software, he explains, to encourage response from users. "It lets them know that someone out there is actually using it."

After trying hundreds of free software packages, both Glossbrenner and Platt rate as most valuable not those programs that compete with commercial programs, but rather "utilities": programs that for the most part have no commercial counterparts. These small housekeeping programs fix bugs in operating systems or do things you wish the program would have done in the first place.

Platt says that NewSweep, a program that cleans up disks, organizes files and squeezes them by as much as 40 percent (allowing you to store more files on a disk and transmit them economically) is "the favorite of everyone who worked on the book." Glossbrenner cites Wash, the IBM equivalent of NewSweep, and an Apple utility called Supermenu as among the programs he could not live without.

Nutting confesses that her favorites tend to be more frivolous. Two examples: Apple II's Monster Maker, in which a mad scientist uses vats of different colors to create a monster (teaching kids fractions along the way), and a music program for the Commodore 64 which, when hooked up to her TV set, plays Bach fugues.