The den in Thomas Throop's Bethesda home looks more like a high-tech studio than the room his family once gathered in to watch television. Sitting on assorted desks and tables are five computers and countless books on bridge.

From that den, Throop, a 51-year-old computer whiz and long-time tournament bridge player, has dealt himself a high-stakes hand, giving up a secure programming and systems-and-analysis career to achieve his fame and fortune as the author of a series of computerized bridge games.

The chances of winning are slim. Each month computer and retail stores are bombarded by pleas from software publishers to add their new programs to the already bulging shelves. In August alone, 126 new products were released.

To get a hit, software authors must come up with a program that either is so innovative or so good that it stands out from the crowd. Then they must get it to market quickly, before some other programming whiz comes up with a better product.

The industry -- born just a few years ago in the garages and spare bedrooms of American entrepreneurs such as Throop -- has now become big business. Large software houses such as Microsoft are competing with even bigger corporations -- CBS, Warner Communications, Simon & Schuster, and Parker Brothers -- for a piece of the estimated $1.5 billion that personal computer owners will spend on software this year.

It is not uncommon, experts say, for major publishers to spend $1 million to $4 million to advertise their wares.

Throop isn't afraid to play a difficult hand. "The way I look at it," he says, "is there are 10 million home computers out there. People say that if you have a pretty good product, it should reach 4 or 5 percent of the marketplace."

With the royalties of $3 to $5 a sale he has been promised, Throop figures he can do quite well by reaching just 1 to 2 percent of the market.

Throop signed a deal with a California software publisher to distribute his first two programs, The Bridge Baron and Instructional Bridge No. 1, to computer stores.

He didn't stop there, though. He also used the extensive contacts he has made in 30 years of bridge playing to have his programs sold at bridge tournaments around the country, and plans to mail notices about his electronic games to an estimated 200 writers on The American Contract Bridge League's press list.

"I'm trying every possible way I can think of," he said during a recent debut demonstration of his programs at the Summer North American bridge championships in Washington.

Roger Hoffmann, author of The Complete Software Marketplace: 1984-85 (Warner Books, $17.95), says most independent software authors won't strike it rich. "It's rare to get $100,000 a year for an independent software program." Nevertheless, he adds, authors with a decent product and a good contract from a reputable software house can make as much as $30,000 a year in royalties.

Hoffmann decided to write the marketplace guide after he plunged, unprepared, into the uncharted territory of software marketing in 1982 in attempt to get an electronic poker game published.

He eventually succeeded, selling the program as a coin-operated bar game and splitting the $20,000 advance and $120,000 in royalties with partner Charlie Nesson, a Harvard law professor and mathematics buff, who originally had written the program to teach his three daughters probability theory.

Hoffman says that, although the market is crowded today, "There are still golden opportunities out there for software authors. There are more and more needs to fill," as the number of people buying personal computers continues to skyrocket and new computers come onto the market.

A growing number of software authors are not the stereotypical "computer nerds," Hoffman reports, but experts in law, education and other fields who bought a personal computer and than began looking for ways to apply it to their own specialty.

Alice Rindler Shapin, 36, of Alexandria, combined her 12 years of experience as a kindergarten and first-grade teacher with her husband Paul's computer expertise to produce Triple Brain Trust, an education tic-tac-toe game that quizzes children in vocabulary, geography, science and other subjects.

They sold that game to Reston Publishing Co. last year and recently have completed work on an as-yet unnamed educational program that will allow children to compose music, draw pictures, and write stories, all on the same disk.

Now, she is hoping the games will be successful enough that the team can produce spinoffs from the spare room in their three-bedroom condominium.

"In the beginning, we thought about doing the marketing ourselves. But it's almost impossible today. The program shelf space is so tight. You really have to fight for it," she says.

The day when independent programmers could develop their software at home, photocopy the documentation, stuff the programs into clear plastic bags and distribute them by mail is over. Today, software packages as slick as best-selling record albums or books have replaced the plastic bags. And high-priced ads in popular magazines and newspapers are standard marketing techniques.

When Lotus Development Corp. introduced its best-selling integrated business package, Lotus 1-2-3, it raised the ante to enter the software game by spending a record-breaking $6 million on development and advertising.

The strategy worked. The fledgling company earned $53 million in sales in its first year. Now the company is promoting Symphony, Lotus 1-2-3's successor, through prime-time television commercials.

Rusty Luhring, a 30-year-old software entrepreneur from Alexandria, remembers when computer buffs could start their own software company on a shoestring. Five years ago, Luhring quit his job, took out a second mortgage and, with $6,000 in hand, founded Ferox Microsystems, a software development and consulting firm in Rosslyn.

The centerpiece of the company was a financial modeling package that Luhring developed and sold for $1,500 a copy. After making his first sale, to the Marriott Corp. in 1980, he began knocking on publishers' doors and eventually turned the distribution rights over to Addison-Wesley, a book publisher just entering the software business.

When the product didn't sell as well as Luhring had expected, he began buying back copies of his own program at a discount from the publishing house and marketing it himself.

He had 30 employees and a thriving business until Addison-Wesley sued him for violation of copyright and unfair competition last year, and he was forced to pay a $100,000 settlement and another $100,000 in legal fees in addition to turning over all rights to the program.

"It was tough trying to recover from that," Luhring shudders. But he stayed in business and developed another business program, Encore!, which he markets himself.

Many new software authors are turning to software attorneys and agents to make sure they don't get burned by a bad contract.

The premier software agent is John Brockman, a once-obscure New York literary agent who became an instant celebrity in the software world when he recently closed a megabucks deal with Simon & Schuster for Typing Tutor III and several other programs by Kriya Systems, a small Chicago software company headed by Sat Tara Singh Khalsa, a turban-wearing member of the Sikh religion.

Brockman won't say how much the deal was for, but estimates by industry insiders put it at as much as $20 million. "It's a wide open field," says Brockman, who reports that his software deals average about $400,000 to $500,000, in comparison to the $25,000 to $30,000 in royalties he usually secures for book authors.

What kinds of programs are likely to be hits? There doesn't seem to be a consensus. But Brockman offers this advice: "You can make money in any market if you have innovative, creative programs."