If the Smithsonian Institution should ever decide to commission a living museum of American folkways and culture, it might do well to consider Prince George's County.

For within the bounds of this gargantuan county, 40 miles from north to south, one finds practically evvery ethnic group, economic class and lifestyle that exists on the American horizon.

Route One might serve as a likely northwest wing for the museum. It is small-town United States' Main Street, as it winds past neighborhood taverns, new and used car lots, city halls and fast-food joints that form the hearts of sleepy little towns like Mount Rainier, Hyattsville, Riverdale and College Park. Its people are the hardware store owners, the insurance agents, lawyers and car dealers.

"This is the common-sense county," says one upholstery store worker with a North Carolina drawl as country music plalys in the background. "We ain't like those folks up in Montgomery, with the whiskey tastes and the beer wallets."

In the northeast wing, the commuter havens of Laurel and Bowie, with their tree-lined streets and quiet neighborhoods, are part of the United States wrought by the automobile since World War ii.

Unlike most of their neighbors on the southern end of Baltimore Boulevard, the residents are largely white collar.

Farther south, down Rte. 3-301, the scenery begins to change taking on the appearance of a hot Southern highway, lined with its own "filling" stations, motels, and tobacco and corn fields. This is the southeast wing of the museum -- home of an agrarian past.

Turning left onto Croom Road, a vistor finds little has changed in this once-proud tobacco land, which still has its one-lane bridges, general stores, barns, farmhouses and green tobacco fields. Tobacco is no longer king in Prince Geroge's, butt it still holds court in towns like Croom, Naylor, Baden, Brandywine.

Farther west, along Fort Washington Road, is the southwest wing of the museum. Here one finds what may be the new Prince George's.

While much of the development that came to this county in the 1960's produced slums in the inner Beltway, in Tantallon it resulted in a prosperous community. Moreover, Tantallon's black and white middleclass inhabitants seem to have come to terms with one another -- at least for the time being.

Finally, we come to the inner Beltway area that has served as a stage for much of the conflict between blacks and whites in the county.

Whether the issue is busing, housing policy, police brutality cross-burnings, or black or white migration, the two groups have always seemed to come up on different sides of the argument: Of all the areas, it gives the best lesson in the sociology of an urban region.

After such a tour, it should not be hard to convince any visitor that this diverse, rough-and-tumble county is the quintessential melting pot.

Though the neighborhoods are not always ehnically identifiable, Prince George's has a population that is one-third black but includes Italians, Irish Catholics, Cambodians, Vietnamese, Anglo-Saxons, Koreans, Philippines, Poles, Hispanos and laotians.

While some of the United States' largest cities may lay claim to a greater ethnic diversity, few if any have the small-town atmosphere of Hyattsville or the farm life of Brandywine.

Nor do many jurisdictions in the country have within their bounds one of the United States' largest insitutions of higher learning, the University of Maryland, a major research center, at Beltsville, and a major Air Force base, at Andrews -- all of which contributes further to the mix of people and lifestyles.

Moreover, this county, known widely as the poor cousin of Montgomery County, has not only the largest group of working-class whites and blacks in metropolitan Washington, but a not-insubstantial middle class as well.

To this reporter, who has covered Prince George's for a year, it also seems clear this same diversity defines the personality of the country, which appears perpetually in conflict with itself.

It explains the colorful shoot-em-up politics that are the norm here. It also explains the Sue Miles and the Larry Hogans -- the controversial County Council member and executive, respectively -- who are such popular figures in their county.

As one council member noted, "in this county, you have to stand above the crowd and take a clear up-front stand or else you get lost in the shuffle. You can't act like a bureaucrat and sound like a bureaucrat and be successful in Prince George's politics. It may happen in Montgomery, Fairfax or Arlington, but not here."

A school board member who has lived in the county about 10 years added, "You have be more politically sophisticated in this county because you are playing to a very diverse audience. You choose sides, and you choose sides carefully, deciding who you don't worry about. You don't have the luxury of being neutral like you do in Montgomery."

Over the years, Prince George's has earned a reputation as a place where the most outrageous things happen, but it also seems to have lived up to its reputation as an all-American county better than any jurisdiction metropolitan Washington.

As one councl staffer put it, "The big reporters who go out to test the mood of the country in Peoria, ill., might do just as well to take a short ride out to Prince George's County."