The last time Nigel Nicolson crossed the Atlantic in search of real America the natives let him down, what?

"I hired a car in Seattle," he said mildly, "and I drove all the way to New Orleans, quite slow, stopping off at universities. I'm very interested in American history, things like the Lewis and Clark trail, and I used to arrive throbbing with excitement about the frontier period only to find . . ." and he paused in the manner of a man who has arrived at Mecca and found the holy men playing Pac-Man, " . . . total indifference!"

Wiser but presumably still throbbing, he has returned with pen and publisher's blessing for a book to be called "Two Roads to Dodge City," a correspondence between him and his 28-year-old son as they travel opposite coasts of the United States and inland to Kansas.

At the door of a friend's house in Georgetown he appeared, 6 feet 2 inches of elderly English ectomorph. Writer, biographer, publisher, former member of Parliament, master of Sissinghurst Castle, true U with his dry, sly Oxbridge delivery, marbled skin and a voice that rises and falls the way an old hinge opens: slowly, dramatically, with feeling.

He's been collecting Rand McNally maps ("I don't think your maps are quite so good as ours -- they leave out all the villages") and reading William Least Heat Moon, keen, as they say, to tell us all about us.

Up early after a night lecture at the National Portrait Gallery, where he had regaled an audience with tales of Yankee heiresses who married nobility, he requested coffee from the maid and stepped down the hallway to a silk-lined sitting room.

"There's a wonderful book I found in New York," he said with the faltering modesty people get when they're about to unveil a find. "It's called 'Bed and Breakfasts in New York.' I'm sure you don't know it."

Politely informed otherwise, he waited while the maid tiptoed in with a heavy silver tray. "On pourrait le mettre ici," he said, motioning the tray to the table. He blinked his slate-green peepers and began again. "Well," he said, "that's the sort of place I'll go. Where you actually meet people. I can hardly stay in luxury because I won't be able to afford it, and in any case I don't want to mix exclusively with wealthy people. I want to go down market."

Not necessarily familiar territory for a 68-year-old who lives in the Elizabethan castle of his childhood and whose literary output most often has been about his very literary past. Mum was writer Vita Sackville-West, daughter of one of England's most prominent families; Dad was diplomat and writer Harold Nicolson.

"Portrait of a Marriage," published in 1973, was based on his mother's diaries, "the story," he wrote, "of twoeseople who married for love and whose love deepened with every passing year, although each was constantly and by mutual consent unfaithful to each other. Both loved people of their own sex, but not exclusively."

"Have you read it?" Nicolson asked lightly. "Don't let it corrupt you."

His mother's most famous conquest was Virginia Woolf, whom Nicolson knew as a kind of visiting godmother at Sissinghurst. The book created an uproar when it appeared; literary figures such as Rebecca West, Cyril Connolly and Bernard Levin called Nicolson a traitor to his parents. A few reviewers accused him of a kind of literary matricide. Nicolson is convinced his mother would have wanted the diaries published.

He has edited six volumes of Woolf's letters and written books about English country houses, the Himalayas, American heiress Mary Curzon (wife of Lord Curzon) and military histories such as the just-published "Napoleon 1812."

His son Adam, also a writer, will begin his sojourn in Los Angeles. Nicolson will start from "Mee-ah-mi."

"I'll write about a Georgetown dinner party perhaps, or I will go to a juvenile court and see how children are treated. Or he Adam might go to a ball game or talk to Mexicans. You know, we'll try and cover a wide spectrum of American life. It will be a sort of discovery of the Americans by two people of two different generations . . . There'll be some leg pulling, of course. I really have to work out the tone of voice."

The vision of squire Nicolson leaving castle walls to wander blue highways and golden arches is one that amuses some of his American acquaintances. He doesn't get the joke.

"After all, it isn't as if I'm going into central Borneo," he said, lifting a cigarette with long fingers thick as penny rolls. "I have been to the States a great many times. Outside Britain I think it is the place I'm most comfortable.

"I guess I am British in temperament. It's a certain reserve, a dislike of exaggeration, which can be anything from loud noise to people shrieking to a building which is too lavishly decorated," he said, loud enough to be audible and not a decibel more.

"I might not be too keen on Coney Island, and I won't go there; I can see myself excited at a ball game. The whole outdoor life of America! I have enormous sympathy . . . for the wild places. And I find New York, with its tall buildings, immensely exciting. And Washington . . . I don't think there's any such city that proclaims its importance with such grace and modesty."

Modesty? The most important city in the most important country on the most important planet in the world? "Yes, modesty. Don't you think so?"

The eagerness to be on the road may account for the brevity of his "Napoleon 1812," first published by his own publishing company, Weidenfeld and Nicolson, in England and just out in the United States.

A slender 182 pages, it is a straightforward, rather remote account of Napoleon's disastrous invasion of Russia, a bloody mess that took 500,000 lives in six months, a series of battles and ignominious retreats Nicolson calls "probably the most dramatic incident in the history of the last 200 years of Western Europe." He began his research intending to write a full biography. "Then I discovered that I would really have to live twice as long as Napoleon to read everything that's been written about him."

Good thing. "Personally, I hate Napoleon," he said. "I think he's a monster. And the more I found out about him, and read his sentimental letters to Marie Louise, his wife, his lying dispatches back to Paris, the more I disliked him."

He is amazed that the French have "forgiven" Napoleon and use his profile to sell brandy and the like. "It makes me wonder how people will think of Hitler in 150 years."

The dust jacket on the American edition describes the book as history in the grand tradition. "Is that what they said about my book?" he said, faintly appalled. "I think that's going a bit far. It's on the blurb, is it? Well, I mean, it embarrasses me. I hope it doesn't compare it to 'War and Peace.' That's the grand tradition, I dare say.

"It must be on the American edition. People in publishing offices always tend to be corrupted by the advertising methods of the movies, where they always use superlatives. Don't pay much attention to that. It's not a claim I make."

There is an English literary tradition for slumming among the Yanks and living to tell about it. Mrs. Trollope, Charles Dickens and Oscar Wilde made the tour in their day; travel writer and novelist Jonathan Raban checked in more recently to write "Old Glory," a sprightly account, marred by the occasional sneer, of his trip down the Mississippi. Nicolson has nothing so nasty in mind.

"It'll be something after that style, though he's not very nice about the American people," Nicolson said. "But of course, he was going through a part of the country where, well, to be frank, there were a great many dropouts. He wasn't seeing the best, was he, of your nation?

"I want, and my son wants, not to set out to praise the people but to illustrate their nicer as well as their seedier aspects. I think Jonathan was rather, well, he was poking fun, See NICOLSON, K8, Col. 3 wasn't he? There was a slightly superior note, to say, really, this is a nation of hippies.

"Which is not so, you know," Nicolson said.

The book will allow Nicolson to resume a correspondence with his son that ended four years ago with Adam Nicolson's departure from university. Nicolson's own childhood at Sissinghurst was Edwardian with a literary twist. The day was carefully planned around his parents' literary activities, he wrote in "Portrait of a Marriage," and the family members saw one another only at meals. Holidays were for studying. Vita Sackville-West's relationship with Nigel Nicolson and his brother Ben was not close. He describes his own relationship with his son this way:

"Our relationship is not in any way sentimental. It's not particularly close because he is married, and has his own son. But we've never had a quarrel. I think it's more a mutual curiosity."

Adam Nicolson's first books were about long walks through the remoter parts of England, France and Wales. The third was the story of a motorcycle trip he made along the Iron Curtain, traveling south from northern Finland. Father expects son to have an easier time chatting up strangers.

"He's very good at picking up acquaintances even though he can't speak the language. That's why he'd be so good for the American book. He can go into a students' place in Bulgaria and within five minutes have a group of young people around him." He said this proudly.

They have $20,000 between them, which must stretch to cover air fare, meals, lodging and their "self-drive" cars. Nicolson pe re has found a congressman to meet. He has secured an invitation to the Kentucky Derby. There is only one thing that can stop them now:

"I was horrified to hear about the slowness of your mail," he said. "Ten days from New York to Los Angeles! Is it true? There really can't be much of a correspondence if it takes three weeks for one to react to the other." He frowned. "I suppose we might use your express mail service."