By Christopher Buckley

 ATLANTIC CIRCLE

By Kathryn Lasky Knight. Illustrated. 222 pp. 

KATHRYN KNIGHT is the wife every yachtsman dreams of. Just after she was married, her husband struck a deal with his acrophobic wife: he'd give up his flying if she'd sail across the Atlantic with him. This thoroughly engaging, funny and beautifully written book is the fruit of that bargain. It is also the product of an unlikely juxtaposition. The author is a woman from Indianapolis who fell in love with a salty blond WASP from Maine. She has passions, from architecture to cooking to literature (and is an accomplished author of children's books); but she really couldn't care less about gudgeons or teak preservation - the sort of things that yachtsmen of the book-writing persuasion tend to dilate on . . . ad nauseam .

The dilations here concern the glories of Mint Milano cookies during freezing North Atlantic gales, or the babas au rhum that ended up looking like ''gangrenous toes.'' (They ended up nicknaming their below- floorboards food storage area La Cote Bilge ). There is also her attempt to buy Tupperware, Sir Francis Chichester's preferred method of keeping the crackers dry, without attending the requisite Tupperware party. Mrs. Knight is a kind of Erma Bombeck of the foredeck.

Her Atlantic is more Walden than a vast expanse of salt water to be crossed, though cross it she does in their 30-foot ketch, and with doughty forbearance. Being out there provides an excuse to write about quotidian things that would otherwise be difficult to package. Who's going to read a book called ''Reflections of a Young Woman Upon Life, Cookies, and Sundry Matters''?

''Atlantic Circle'' is also a travel two-fer. Once across, she and her husband spend some leisurely months taking the boat through the canals, locks and rivers of Denmark, the Netherlands and France. It is a fragrant and mouth-watering journey that winds through Bocuse and Burgundy country, and has the effect of washing off the trans-Atlantic salt. It would also be a good guide for anyone contemplating the same trip.

Among her many endearing qualities is Mrs. Knight's distaste for the ''enhulled'' people who spend their whole lives on boats. It's not that these people love the sea, she observes; they simply can't get along ashore. She is especially adept at skewering the kind of yachtsmen who consider toilets a ''lubberly feature'' and who admonish their guests - guests! - to employ the pages of their (own) books for hygienic purposes.

''The biggies, like Hitler, Mussolini, Nero have been enshrined in the darker pages of history,'' she writes. ''But the petty tyrant too must be reckoned with. Although he or she does not plan the extermination of a race, it is the petty tyrant that day in and day out causes the thousands of small deaths of the spirit of the people closest to him or her. And it is these small deaths that wear one down until a person is a mere shell, a husk of a former self through which the wind can moan.''

This is a wonderful passage to come across in the middle of an ocean passage, and of a piece with this wise and companionable woman.