Paul Theroux; Charm to wobble you out of your armchair

''Well, I wanted to write,'' Paul Theroux remembers. ''You hope good things are going to happen to you. . . . I thought that my career . . . would have something to do with travel; teaching, probably. I hoped that I would marry and have children, something like that, you hope for the best. . . . You know that you're going to write, but you never really know about publishing books or what people's opinions are going to be.''

His hopes came true. He taught for 10 years in Africa, Singapore, and Italy, married an Englishwoman he met in Uganda. He lives in London with her and his two sons, and as for publishing books, Houghton Mifflin has just published ''The Mosquito Coast'' (Boston, $13.95), his 18th. People's opinions - the critics', anyway - are adulatory.

As if that weren't enough, he told an audience at the Boston Literary Hour that, for him, writing is actually pleasant. ''People talk about the pain of writing, but very few people talk about the pleasure and satisfaction. . . . The pleasure a reader gets is often equal to the pleasure a writer is given'' in writing a book.

With all this talk of hopes fulfilled, cooed in the most quiet and cultivated of British tones (even though he was born in Medford, Mass.), one would expect the audience to get cranky and ask questions designed to disprove everything he said. There were a few of those, but most of the time everyone was entranced. The crowd interrupted his speech on travel and the novel - a witty bundle of insights, jokes, and asides looped together with a quiet, self-satisfied smile - with purrs of applause and laughter.

Speaking to a crowd or in an interview, Paul Theroux has such charm that you only want more of his good things to happen to him so that he can tell you about it. And whether he hoped to be or not, he is handsome in a way that even the striking book-jacket photos of him don't prepare you for. The sleek, dark-haired traveler standing by train tracks on the back of ''The Great Railway Bazaar'' doesn't hold a candle to the man in the conference room of Houghton Mifflin. In real life his eyes are brown and look away with an appealing pucker of his long, Gallic eyebrows, while he considers a question as if the interviewer were the only person who had thought of it. He makes a stop on a national book tour seem like an hour of sparkling literary conversation.

He takes such delight in being a writer, teacher, father, husband, and traveler that he seems briefly to take a listener along with him. Hearing him talk cheers you up the way reading a book in which everyone lives happily ever after does.

''The Mosquito Coast,'' however, is not such a book. It is a terrific story, but it comes to a very bad end. Allie Fox, Yankee inventor and cranky philosopher, gets so disgusted with the way the United States is going to the dogs that he picks up and moves to Honduras with his wife and children. It is a father-and-son adventure story, which Theroux wrote for his sons, Marcel and Louis.

''Mosquito Coast'' is dominated by Allie Fox's squawks of disapproval. He doesn't like waste or junk or much that has happened in the US in the 20th century. He doesn't like laziness - in Honduras, he won't eat bananas because that's too easy - and he doesn't like timid children. He is an inventor's inventor, who sees the world as a mistake God made, which he luckily came along to fix. With a kind of pity, he calls the Honduran migrant farm workers on the farm in Massachusetts ''savages.'' He can't believe they would leave Central America, which he considers a far superior place to be, because it is an older ecology with underground steam that could be harnessed. Such things appeal to efficiency-minded inventors. He gives the workers one of his inventions and tells them he'll trade places with them, adding sadly to his wife that that's all they have to trade.

Theroux, another kind of inventor, chose Honduras because ''I wanted to find a place that was as wild as possible and as empty as possible and yet still about an hour from Miami by plane.''

The book is compelling to read, because Theroux's charm also inhabits his writing style. And also because it is narrated by Charlie Fox, Allie's 13 -year-old son, who is as doubting as Allie is boastful but who loves him with all the complicated earnestness a son could give a wild father.

Walter Clemons in Newsweek described it as ''a work of fiendish energy and ingenuity by a writer whose cleverness is matched by his enjoyment of his own virtuosity.'' This cleverness and enjoyment are, likewise, available to the reader.

Writing from a 13-year-old's point of view forced Theroux, a world traveler who's already been everywhere, to look at the jungle in Honduras as though for the first time. He found it satisfying. ''I think a character that isn't particularly literary . . . evolves a kind of imagery that's useful. The imagery of the book is deliberately 13-year-old imagery. He describes a man as 'he looked like a dog hearing a door slam.' It's the sort of watchful look that a dog has with the ear cocked and the sort of face that's vaguely smiling. It's not a smile, it's sort of apprehension. A child would think of that, but it's hard if you're writing a novel to say . . . something like that.''But Charlie wasn't enough for that fiendish energy and ingenuity. There had to be Allie Fox, another voice entirely. ''I didn't realize that the father in this book would be as important or loom as large as he did when I started it,'' Theroux says. ''When I was writing, I saw that the child's vocabulary was small, and to maintain my interest in it and actually to give the novel its full scope, the father has a tremendously large vocabulary. I mean, the father talks about 'postprandial glissades,' he . . . uses words that no 13-year-old would know. . . . That's one of the pleasures of this novel, actually, to me, that the child is talking in one voice, the father's talking in another.''It is no accident that he read ''Huckleberry Finn'' before writing this book. But even though both boy narrators are 13 years old, the parallel is not meant to be between Huck and Charlie, he says, but between Huck's father, Pap, and Allie Fox.Fox shares Pap's impulse to bolt the country, Theroux points out. ''Call that govment!'' says Pap in ''Huckleberry Finn,'' ''A man can't get his rights in a govment like this. Sometimes I've a mighty notion to just leave the country for good and all.''Allie expresses himself a little differently, railing against his boss, a Polish farmer for whom he is handyman and inventor. Allie is sick of ''all these fake frontiersmen with their chuck wagons full of Twinkies and Wonderbread and aerosol cheese spread. Get out the Duraflame log and the plastic cracker barrel, Dan, and let's talk self-sufficiency!'' He actually does leave the country for good and all, unlike Pap and the Americans Theroux has heard complaining. ''I think the informing notion in the book is that very, very strong desire that Americans get or have gotten lately, that this isn't the country that it once was, that something has happened here to society. . . . I started hearing people saying, 'I'm fed up, I'm fed up,' and it wasn't the same thing people were saying before in a joking way; . . . you know, 'things ain't what they used to be. . . .' '' Theroux was hearing these mutterings on trips here from London. He spends at least four months of the year in this country, and says it's ''where I'm happiest,'' but lives in London because his wife works for the BBC. And he feels that visiting off and on lets him be much more objective about American life - he isn't caught up in it so he can observe swings of public opinion.Of course, Theroux himself has acted on yearnings for foreignness that the rest of us just shuffle to the back of our minds without so much as twitching in our armchairs. He began the trip across Europe on the Orient Express and back to London on the Siberian Railway (which became ''The Great Railway Bazaar'') because he had a cold. ''That cold made leaving all the easier; leaving was a cure. 'Have you tried aspirin?' 'No, I think I'll go to India,' '' he wrote in the opening pages. In ''The Mosquito Coast'' as well, he gives the sedentary but yearning readers an outlet, and answers the questions that begin ''what if I just . . . .''In Honduras, the Fox family settles in just like the Swiss Family Robinson. Allie organizes them and the natives into building a rainproof house with a porch made of bamboo trunks, a vegetable garden of super hybrids brought from Massachusetts, a pump that runs on water power, a clean latrine, and, finally, Allie's prize invention, a machine that makes ice from fire. There are always the verbal inventions, oral runoff of Allie's colossal energy. As he and Charlie and two Zambu Indians are hiking over a mountain, towing a huge block of ice Allie has made to deliver to more primitive Indians, he says to his sons and the Zambus, ''We'll have lunch on top. Then we'll have a lovely postprandial glissade behind this baffle and sock this frozen monolith into that benighted wilderness.'' He winks at his son and says, ''You've got to talk their language.''Which he never does. He talks his own language - a lot. He constantly orders his children and the natives around, and even though he does so in his own convoluted, black-humorous philosophical style, he gets a lot of cooperation. He demands more than just cooperation from his children, especially Charlie; he wants their enthusiasm for his world view. They are his disciples. ''Admit it,'' he says to Charlie, ''this is better than school.''Though Allie Fox is bizarre, he is also appealing. He seems to have a weirdly common-sense solution to any problem. He is constantly in motion, inventing things. Theroux expects him, with his inventiveness and fast talking and his grudges that make some sense, to speak to readers. People threaten to leave the country, but, ''Well, this man alone among all the others is actually doing it, so he in a sense is doing it for the reader.''

Actually, Theroux is the inventor, and he's doing it to the reader. After the peaceful progress of the Swiss Family passage, all goes wrong. Allie's invention literally blows up in the family's faces, and in ours. The hopes of starting over again in a new and primitive land (at one point Allie claims to have taken their settlement from the Stone Age to the Iron Age in a month, promises to reach 1832 in a couple of days, and skip the 20th century) and, incidentally, help the natives to free ice comes to naught. Armchairs will wobble with shock. ''Mosquito Coast'' may begin like a travel book, but it turns into an antitravel book.This is a story with a stern moral: For all the traveling and free ice, Allie Fox is no more about to change than life in Honduras. ''You can't leave, you can't hide, you can't escape,'' says Paul Theroux pleasantly. ''You go to a place and you say, 'We must start all over again,' but you take yourself with you . . . it's part of your baggage, all your neuroses and flaws and weaknesses as well as all your strengths. You're starting off in a different place but with the same raw materials. So a person reading it sees all this happening, is thrilled for about three-quarters of the book, and then sees where it tends. You can't leave all this behind.'' In its written form, Theroux's pleasant voice, like anything charming, charms for a purpose. He pulls readers into the excitement of his revisionist creator so they don't see the downfall coming. It's a well-made booby trap.Regardless of a grim ending Theroux says, ''There's nothing in this book that any intelligent child of 13 would be put off by or would find strange.'' He wrote it that way on purpose. Charlie Fox and his little brother Jerry are the same ages, 13 and 11, as Theroux's sons, Marcel and Louis. Until this one, they had never read a book by him, though they hear from other people all the time about their father being a writer, and ''they have no comeback.'' Theroux thought reading ''The Mosquito Coast'' would give them a comeback, as well as an enjoyable experience.''They could say 'yes, I read this book,' and they could say whether or not they liked it. Of course they would, I suppose, defend me, but they would feel as if they were a part of that opinion.'' They might feel independent of their father's inventions, an independence the Fox children achieve only at great cost.Though the book will give readers of any age nightmares, he maintains that children ''might be relieved'' by the way the book ends. Whatever the reaction - and the Theroux children have read the book and liked it - Charlie Fox is as good-hearted a character as will ever tell you a story. Whatever his father is doing, he loves him, which becomes a burden as he begins to see through the self-promoting chatter and feel trapped in the jungle. His narration is more than a simple voice and fresh visions. It is straight from the heart, and even though he often despairs of his father, his love for him informs the book. Jerry Fox, the more skeptical younger brother, rings true, and Mother, a silent but comforting presence whose short, sensible objections sound like aphorisms compared to Allie's speeches, anchors the family in sanity. Allie Fox's best observer is Charlie. He sometimes sounds older than 13, but you would too if you had gone on that trip.