In his brilliant book "Abroad," Paul Fussell mourns the replacement of travel by tourism. "I don't want to sound too gloomy," he writes, "but there's a relation here with other 'replacements' characterizing contemporary life: the replacement of coffee-cream by ivory-colored powder, for example, or of silk and wool by nylon; or glass by lucite, bookstores by 'bookstores,' eloquence by jargon, fish by fish-sticks, merit by publicity, motoring by driving . . ."

As a corollary, he finds that the ship has been replaced by the cruise ship, though at least that is preferable to a plane: "It is healthier because you can exercise on it, and it is more romantic because you can copulate on it."

The book, in some ways an outgrowth of his equally brilliant "The Great War and Modern Memory," celebrates the great lemming-rush of literary Englishmen to the Mediterranean and the Greece they had studied in school, to any place warmer and brighter than England itself or, more to the point, than the trenches of World War I.

The people of other countries joined the rush, of course, but they seem to have written novels (Hemingway and Fitzgerald come to mind), while the English wrote travel books. Fussell explores with wit and painless scholarship the difference between the two genres and decides it is crucial for the travel writer that the reader believe these things actually happened to him. (One is not being sexist here; they were, almost to a man, men: Durrell, Huxley, Graves, Maugham, Russell, Douglas, Spender and others, and Katherine Mansfield.)

Something about the heat and the light, the palm fronds and glittering sea, unhinges the proper English, making "even so phlegmatic and civil-servant-like a soul as R. H. Bruce Lockhart suddenly come alight and blurt out that the Mediterranean Sea has 'more history in one of its waves than the Atlantic has in the whole expanse of its 24 million square miles.'"

An exception was W. H. Auden "who carefully kept his skin its original ghastly blue-white." But the others found in the sun an antidote for gray British hypocrisies.

Another modern excrescence is the passport, which Fussell traces to the barbed-wire Western Front, leaving us with the notion that "a frontier is not just absurd but sinister" and helping to replace the insouciant traveler with the anxious tourist.

Along the way, the 56-year-old Rutgers professor, who visited here yesterday, treats us to the offhand bon mot. "The weather of Boston, New York and Washington is so bad that if the United States had been colonized from west to east instead of the reverse, the northeastern United States today would be populated as sparsely as North Dakota.The main cities would be somewhere else, and the northeastern area would be planted out in soybeans."

Where has this original spirit been all our lives? Mostly teaching 18th-century literature at Rutgers. And traveling. Summers, he and his writer wife Betty Ellen take off. They used to take their son and daughter along, when that was practical. This summer they hit eastern Europe ("I wanted to avoid the conventions at all costs."), took a train from Budapest to Auschwitz to get a sense of what the Holocaust victims could see through the slats of their cattle cars ("beautiful, simply beautiful countryside, so ironic").

He has German, with some Italian and a bit of Greek and Turkish and enough Russian to insult people when necessary. She has good French. They still haven't seen much of South America; would like to try China.

"Everyone has the same desires these days. Prague looks just like Houston. There is, of course, Islam, where they want to be right rather than rich. That might be interesting to see."

Meanwhile, he has been boning up on the South Pacific for a book on World War II due by 1988. As an infantry lieutenant in that war (Bronze Star, two Purple Hearts), he fought in France but just missed the Pacific war.So he has been systematically visiting the battle sites there, from Tarawa to Okinawa. Before he starts writing that one, however, he will put out a collection of essays, "The Boy Scout Handbook, and Other Observations," defying his own theory that the essay is obsolete except when disguised as travel notes.

While the package tourist takes a terrible riding in "Abroad," as might be expected, Fussell also elegantly skewers the anti-tourist, the kind of snob who goes to England to visit, not Westminster Abbey, but Chiswick House, who never carries a camera, who goes by tram instead of taxi, and so on. He confesses to be a little of both.

He also sees a relationship between tourism and "the C-plus university," where student minds are Simonized rather than educated, where curiosity, the hallmark of the intellectual, is ignored if not actually discouraged. This, he says, is what this book is really about: travel as a metaphor for intellectual energy.

A question for the curious: Why exactly is it that we abruptly abandoned the belief that "to omit one's solar topee for only a few minutes was to invite madness, 'brain fever' and death," and took to sun worship even to the point of skin cancer? The who Western world reversed itself on this important issue in just a few years. Interesting.