The huge swing, a deceptively simple-looking contraption of brightly painted poles and triangles, hangs quietly from two towering trees in the Falls Church backyard of Marion Lelong. But only momentarily.

First one neighborhood youth climbs abroad, his feet braced on one of the two wide seats. And then another. And another. And another. Lelong gives a shove, ducks his head, and the swing begins its wild sweep around the yard, dipping and sailing and twisting forward and back, sideways and skyways.

It's an unusual swing -- able to hold a half-dozen or more people -- and one you're not likely to see anywhere else. Lelong built it for his children, and it has become a popular neighborhood attraction.

Lelong has obtained a patent on the swing and thinks there might be some money to be made in manufacturing and selling it, perhaps for playgrounds. But so far, he's been unable to interest the business world.

In that Lelong is not unusual. It's a long, sometimes costly and often disappointing road from inventing something and taking it through the patent process to realizing any money from it.

And Lelong, 58, is one giant step ahead of most of the country's individual inventors who work for their own fun (and sometimes profit) instead of for corporations or the government. He's patent attorney, accustomeed to shepherding other inventors down that long road.

"You've got to be an entrepreneur as well as an inventor to make a success out of a patent," says Lelong, who figures his swings might sell for $250 each if he could find someone to manufacture and mass market them.

Bethesda inventor Jacob Rabinow, 69, agrees. He's made money and he's lost money on what he says are 3,000 inventions developed over a lifetime, more than 200 of which he has received a patent on. Inventing is "a gamble," he says. He estimates only three or four individuals in the country can actually live off their inventions.

Rabinow's patents cover a wide range of technical devices, including a record player marketed by Bang and Olufsen (on which his 17-year patent has expired) in which the arm moves across the platter in a straight line. But inventing has only been a sideline to a career as chief research engineer of the Bureau of Standards Institute of Applied Technology, from which he retired in 1975 but where he still shows up several days a week.

B. Edward Shlesinger Jr., 55, is another local patent attorney who has had mixed success in marketing his new devices. He got his first patent on an adjustable stapling machine that could accommodate larger sheets of paper and sold it to Bostich. Electrical connectors he developed are on the market in large quantities. But he had the bad fortune of coming up with a top-loading fountain pen (to keep your fingers out of the ink) -- which caught the eye of Scripto -- only to see its chances on the market wiped out by yet another novelty, the ballpoint.

Yet, despite all the difficulties, there are fortunes to be made. Individuals have prospered on such diverse brain-children as the helicopter, the Polaroid Land camera and the "Slinky" toy the coiled spring that walks down stairs. It's surely that dream of making it big that keeps the patent applications pouring into the Commerce Department's Patent and Trademark Office in Crystal City at a rate of more than 100,000 a year, about a fourth of them filed by individuals.

To Rabinow, the individual inventor is the backbone of America. But he sees this country's technological superiority being overtaken by foreign competition. And he blames in part the conglomerates which he feels are too big to be innovative or to pay attention to the technical quality of what they are selling. "The country needs inventions very badly," he says.

Adds Isaac Fleischmann, director of information services for the patent office: "We're in a terrible bind now in energy. Never before has it been so important for use to have inventions so meet these needs."

So in the back of your mind, you've got an idea for energy development or saving. Or maybe an idea for a garden tool, a kitchen gadget or a toy that you've never seen on the market. How would you go about getting it patented and perhaps even making some money?

Shlesinger, who is convinced inventing can be learned, has developed a new filmstrip program for schools, "The Art of Successful Inventing," with Prentice Hall Media. Among his keys to inventing: Stay alert to areas of need, such as complaints, difficult or inconvenient situations, or recurring breakdowns or injuries. Think of something that might eliminate those problems.

If you decide you've got a saleable invention, the patent office advises you to get professional help in filing an application for a patent. The documents are highly complex. The patent office can supply a list of the 10,000 patent attorneys or agents nationwide who are registered to prepare such applications. An attorney may cost you $1,000 or more depending on how much work is required.

The basic application fee is $65, but there are additional costs as the application is processed.When received, the application goes either to a chemical, electrical or mechaniccaal examining group, where the patent office's more than 1,000 examiners research millions of U. S. and foreign patents to determine if you are entitled to a patent. More often than not, the application is rejected the first time, and you are given a specified amount of time to answer the examiners' objections.

If you are successful in the next try, you will be granted a patent for a period of 17 years. About 30,000 to 40,000 applications are rejected yearly, according to Fleischmann, and the average processing time is 20 months. Lelong estimates his patent office fees for his swing at more than $450.

Once you've got your patent, you are on your own in trying to cash in n it. Lelong and Rabinow say the best way is to start your own business and get it going, and then the big companies can assess it. Other alternatives, suggests Shlesinger, include knocking on the door of any company you think would be interested in adding your invention to its line, or soliciting investments from your friends and acquaintances and then hiring manufacturing and marketing experts to develop your company.$ even if you don't make big money or any money, there are other rewards to inventing, says Rabinow. "It's exciting, and occasionally you do change things." CAPTION: Picture, Marion Lelong demonstrates his swing and gives neighborhood children a ride. Photo by Lucian Perkins -- The Washington Post