They're calling it Amway Mansion here in the Northern Neck and the talk, in this region of knee-high wheat and oyster-shell roads, is filled with curious imaginings.

The structure is owned by a soap magnate, one hears from those who live here year around, a man in many minds not unlike the model for Citizen Kane, who can mix baroque and modern, towers and spiral stairways, who is building himself a castle on the banks of the muddy Yeocomico River.

They have never seen him, but he must have a certain flare, definitely East Egg as opposed to West although, like Gatsby, he has chosen a place across the river from more fashionable shores.

Rumor has it that he will visit for just several days a year and that the parties will be lavish, perhaps with nymphs on the sun decks and men with tailored moustaches doing flips off a diving board into the pool.

In fact, the mystery man of the mansion is an Amway distributor. His name is Rex Renfrow. He is 50 and he lives in Fairfax County. He is building himself a large house in the country, but his roots are on a tobacco farm in Johnston County, North Carolina. And he was not always rich. Before he made his first $28 investment in Amway he was a bureaucrat with the Department of Agriculture, a man with a high-school education who worked his way up in 21 years from a clerk-typist to a GS 14.

Renfrow agrees that his new place is somewhat lavish: 7,200 square feet of house perched on pilings, built for an amount that he prefers not to disclose. And it is true that he will not live there full time. How much time he will spend there he also chooses not to disclose.

But he will be spending some time in the Kinsale home, which has the the same cedar shingle roof, lattice work, tower-equipped feeling of expansiveness as his estate near the Occoquan Reservoir.

Renfrow said that he heard about the area from a United Airlines stewardess on a coast-to-coast flight. He liked the "friendliness of small-town people," the price of the property, and the "flexibility of shade," even though his wife, Betty Jo, wanted a place on a sandy beach.

As for the parties, he indicates that the Kinsale house is likely to see more fishing poles than champagne. It will be a place where his parents can spend time when he is not there, Renfrow explains from his desk, behind which hangs a sampler that paraphrases Dorothy Parker: "The Difference Between Men and Boys is the Price of Their Toys."

As Renfrow sees it, his home on the river is simply a retreat, built with intentions "no different than if I ran a grocery store downtown and chose to build on the water."

But the people of Kinsale do not know any of this yet.

Ellen Hinson, a 23-year-old Kinsale resident, has been to see the mansion. She met a friend at the Kinsale Market one day and, fortified with the curiosity of two, they got in the car and drove up to the driveway. It appeared that no one was there, but they hesitated to go any closer.

"No," says Hinson. "Nobody's seen him yet. They said he was in town last week, but I didn't see him."

Johnny Wayne King, 23, who has been up to the mansion, says: "It's big, I can tell you that."

Not that the people of Kinsale are worried that the arrival of a mansion will change their world. Curious imaginings are a far cry from nail-bitten speculation. This, after all, is a town of 500 in a county with a rich history of its own. Times never have been really good for very long around here but, like a man with a title but no money, Kinsale has a sense of its own tattered nobility.

After all, George Washington, Robert E. Lee and James Monroe were born here. And buried here, figuratively speaking, is the father of Dick Diver, a character in F. Scott Fitgerald's "Tender is the Night." And although Fitzgerald never slept here, writer John Dos Passos spent boyhood days here.

Dos Passos was known as Mr. Jack when he returned in later life to the land of his childhood. He remembered the "tobacco-exhausted land of the Northern Neck," during times that were perhaps Kinsale's worst: the early years of this century when, " 'round along the rivershore past Harmony Hall," lived people such as "Sydnor, a big six-foot-six barefoot man with a wart on his nose...ashamblin' around and not knowin' what to do on account of the drought and his wife sick and ready to have 'nother baby and the children with hoopin' cough and his stomach trouble...

Kinsale today has one store and a post office. It is a place, says Northern Neck writer Walter (Pete) Norris, "Where there's very little left but fantasy."

So the people of Kinsale continue to speculate, even though Renfrow does not think that building a large house is much of a big deal, just a man spending money that he has earned.

"My wife and I both worked hard to have what we have . . . to make some of our dreams come true by working," he says.

"It would be rough," says Northern Neck resident Wayne Lawson, working with a hammer and nails on the third floor of the house that he knows as the Amway Mansion. "But I think maybe I could handle living here."