George Robberecht of Colonial Beach, Va., raises eels. Hugh Lesley of Oxford, Pa., collects Edsels. Bill Steed is a doctor of frog psychology at Croaker College in Sacramento, the world's only institution for the education of frogs, Elmer Gardiner is a good-humored grocery-store owner in Nayaug, Conn., who once ran for president, promising to ban pay toilets.

Jamse Dale Davidson came across these four and scores of others with equally unusual interests when he went around the country writing "An Eccentric Guide to the United States." Davidson had in mind what John Stuart Mill meant when he said: "Eccentricity has always abounded when and where strength of character has abounded when and where strength of character has abounded; and the amount of eccentricity in a society has always been proportioned to the amount of genius, mental vigor and moral courage which it has contained."

By that definition, eccentricity should be flourishing in America as much as apple pie, hot dogs and certain automobiles. But Davidson wondered if eccentricity hand't died. When you're around Washingtong long enough, you don't get the feeling that Americans are basically eccentric.

More than that, Davidson had collected some alarming data suggesting that eccentricity might be in trouble. A free-lance writer from College Park (he holds bachelor's and master's degrees from the University of Maryland), he also works on Capitol Hill for the National Taxpayers Union, a public interest lobby.

Davidson sees Americans being taxed into submission - a condition guaranteed to stifle creativity and anything eccentric.

"There's a total squeezing out of the middle class," he says - enough to sap its courage and vigor. "With the bureacracy growing, taxes going up, you reach the stage where everybody is getting poor. In 12 years, the individual will have only half the real income he has today to spend.

"Tax laws are designed to immobilize capital and discourage investments. They make you borrow, make you go into debt, they want you on a hook. There's nothing worse than being dependent. The government is confiscating the potential capital that would make the middle class independent. We're eradicating independence.

"I can't believe Americans are going to take this lying down forever. It's the most important development since . . . since . . . really forever."

So Davidson is writing another book called "The Squeeze," about the woes of the middle class, but before that he wanted to make sure the middle class was still out there, struggling. Thus, he drove 25,000 miles, the result being a 500-page paperback full of insights into the 50 states and the District and the people in them, brought out last August by Berkley Publishing Corp., of New York.

Davidson - who is 30, single, and says he paints and reads for leisure, and runs 340 days a year and swims the other days - packed up and went searching for those people who are creating that which is "wonderful, in true sense of that much abused word, and interesting and fun in America."

"I wanted to see the country," he says, "not in the sense of standing in line at Yellowstone but to look at America as it might be - a place where there still is some potential. There are people out there I would call real Americans - who have taken advantage of their potential to do creative, interesting things.

"Some people have think they know America. Mention Alabama, they think of George Wallace. They don't think of the Ave Maria Grotto," which incorporates 50 years of work by Brother Joseph Zoettle of the Order of St. Benedict, who built 150 small-scale, detailed masterpieces such as the Hanging Gardens of Babylon and Rome itself.

Seven miles west of Madison, Wis., Davidson came upon the works of Bruce Baldwin Mohs, described in the "Guide" as "a slightly eccentric millionaire inventor." He has invented a number of motor scooters, a "Swing-and-Sway" tractor seat, an aluminum bicycle pedal, and the one-and-only Ostentatienne Opera Sedan - with "not one model sold," Davidson reports. "In the rare event that someone would be entering (one), the feat can be accomplished only by crawling in through a wide opening in what would normally be a trunk."

G. F. Gailor's Hubcap Garden near Saratoga Springs, N.Y., features hubcaps stuck on fences, poles, trees, "catching the light of the sun," says Davidson. "It's not high art, but it's art." In Fulton, Mo., he discovered Jesse Howard's Windmill and Graffiti Factory. The windmills have Bible verses painted on the vanes, the hand-lettered signs "recount the themes he wished to explore in his never-held-audience with President Eisenhower." (White House guards didn't have time for this eccentric, born in 1885, and packed him on a bus back to Missouri, according to Davidson.) Howard gave Davidson a large cantaloupe.

In Minnesota, Davidson found one Fred A. Johnson making the world's largest ball of string - now 11 feet in diameter and weighing 10,000 pounds. In Vermont sits the largest chair, weighing more than a ton; in Massachusetts, a 42-pound lobster resides. Davidson figures if there were ever any larger it would have been displayed only briefly in drawn butter before being eaten.

Reasured that Americans' ingenuity persists, Davidson now is hard at work on "The Squeeze." In attacking tax oppression, he wants to do his part to make the country a place where the Jesse Howards and G. F. Gailors can flourish.

Davidson also is working on a play, "about Washington and its illusions" and an "unhistory" of the United States.

"This will tell of things not in history books," he says, "but things that figure more importantly in people's everyday lives than kings, battles and plagues, which seem to be the main part of traditional history. For example, Santa Anna is remembered for the Alamo but in unhistory he was the precursor of Wrigley's gum. To finance his comeback as dictator, he tried to galvanize chicle to be used as tires; chicle could be made hard, but as soon as he wet it it became soft again."

Just the type of thing to interest your average American eccentric.