Mark Stoughton was waiting for some wide-eyed myth of an American inventor with a bag full of mind-boggling inventions to walk into his classroom.

So when Bill Shlesinger arrived in a conservative gray suit, with only a book, a set of color slides and no evidence of any loose gears, 12-year-old Mark was unimpressed.

"I expected somebody with wild hair from some basement laboratory," said the sixth grader at Laural Ridge Elementary School in Fairfax. "Some old guy like Thomas Edison."

Shlesinger may not fit the stereotype, but the 55-year-old Alexandria patent attorney is a certified inventor. He has 118 of his own patents, most dealing with electric switches, and some that have earned him money.

Recently, in front of 40 Laurel Ridge students, Shlesinger was playing teacher. For 90 minutes, using a color slide and cassette program based on his book, "The Art of Successful inventing," Shlesinger taught inventiveness as a gift of ordinary minds. Being odd and disorganized, he said, is no prerequisite.

"Inventing has always been done by people considered to be eccentrics," admits Shlesinger, "but almost anybody can invent if shown how. That doesn't mean everyone is going to be a topnotch inventor. But you can teach somebody to play the piano, for example, who's tone deaf."

Shlesinger approaches inventing the way a systems analyst would tackle a logistics problem. His technique is methodical, logical and directly contrary to the much-loved and largely false idea that invention depends upon late night thunderbolts of inspiration.

Shlesinger has taken his "everyman an inventor" theory beyond his Crystal Plaza patent office. During the past 10 years he has taught business exectives, engineers and students, from elementary school to college, how to be more inventive. His book, published in 1974, is currently listed in the curriculum guide for all Virginia public high schools. c

The biggest test of his technique says Shlesinger, was a five-year teaching stint, from 1969 to 1974, at the District of Columbia's Lorton prison complex.

"I figured if I could make these fellows learn it, many of whom couldn't read or write, I really had something." Shlesinger says his teaching techinique passed with honors. Lorton officials confirm that his course was "popular" and "productive." And while none of the inmates changed the American way of life with their brain storming, Shlesinger says that was not his ultimate aim.

"The real benefit of being inventive is learning how to solve problems. There are thousands of problems facing everybody and they just don't recognize they've got the solutions."

Shlesinger's work has impressed more than his students. Last year Prentice Hall Media, one of the largest publishers of educational material in the world, developed a color slide and cassette program based on Shlesinger's book.

"He's an unusual author for us in that he doesn't come out of the educational community," said Karen Miller, vice president of Prentice Hall, which has marketed the teaching progam for $82.

Shlesinger's educational program is designed for high school students, but little of it went over the heads of the elementary students at Laural Ridge. The 40 students, a collection of third to sixth graders in the "gifted and talented" program, grasped the concepts faster than Shlesinger could throw them out.

"They sit around the lunch talbe and talk about Iran, the problem with the Soviet Union and the effect of invention on inter-personal relationships," said Susan Akroyd, coordinator of the gifted and talented program. "I have to do a lot of research on my own just to keep up."

In his lecture, Shlesinger used a chalkboard eraser as an example of a product that could be improved, but the students went even further and talked about such things as solar powered heating systems.

This year's class project for Akroyd's precocious kids is inventing. They have already visted the U.S. Patent Office and have planned an inventors' fair.

"I've been experimenting with ideas on using the ground as an insulator," said fifth grader David Bulova, who intends to be a 21st century architect. Other students have been working on more efficient solar powered batteries and remote control light switches.

Marc Capponi and his sister Debra have invented what they consider to be a better mousetrap, using wooden rulers and a hinged door.They haven't worked out all the "bugs" in their trap and, given the realities of the business world, they aren't sure they ever will.

"If you invented something when you're only 11 where would you go with it?" asked the market-wise Debra.

"Besides," added Jeff Gregory, "everything's already been invented."

"It only seems like that," answered fifth grader Kyle Anderson, "until you invent something."