IN THE YEARS SINCE turning from her earlier, Japan-based novels (mostly notably the award-winning The Master Puppeteer), Katherine Paterson has created a handful of engagingly rakish young Americans. The two mavericks of Bridge to Terabithia and the incorrigible title character of The Great Gilly Hopkins are spunky, independent, and sharply observed. Both books won several kinds of prizes each, but my own private prize goes to Gilly -- always a foster child, never a daughter. I'd adopt her any day.

Jacob Have I Loved, Katherine Patersons's sixth novel, centers on an ugly duckling of such endurance and rough charm that readers should take to her immediately. "Wheeze" Bradshaw is a twin -- a second-best twin. Her sister, Caroline, is pretty and supremely talented, while Wheeze is a gawky girl of no apparent talent at all, unless you count her considerable skill as a crabber and oyster tonger off Rass Island in the Chesapeake Bay.

Without even trying, Caroline acquires everything Wheeze wants. She isn't a villain, however, and this is not a stereotypic good sister/bad sister story. It's convincingly complex, ambiguous. Caroline can be a prig but she's also kindhearted. The parents do their best to be fair, although they don't <(CONTINUED FROM PAGE 11) always succeed. And when Caroline makes friendly overtures to Wheeze, it does not (to our relief) result in magical harmony forever after.

The book opens in 1941, when Wheeze is a scruffy 13-year-old poling a skiff with her only real friend, a boy named Call. It continues through the war years, during which Call joins the Navy, Caroline sets off for an exciting new life on the mainland, and Wheeze quits school to help her father on his boat. Tough and weary, wearing men's clothes, she makes a fascinating heroine. We'd been expecting something different -- one of those overnight transformations. But Wheeze just plods along, smelling of crabs and sea-water, and when Call comes home it's not to stay with Wheeze, after all, but to announce his engagement to Caroline.

Shortly thereafter, Wheeze decides to assume responsibility for her own life. She leaves the island to be educated, takes a nursing job, marries, and plays midwife to a set of twins who teach her something about her own twinship.

If the paragraph above seems abrupt -- all the long, slow, growing-up period followed by slam, bang, married-and-settled -- well, it's because at this point the book itself becomes abrupt. That, I think, is its one flaw: there's a change of pace that's difficult to adjust to. Leisurely details give way to summary. There's not the same deep texture that existed in the earlier scenes.

But oh, those earlier scenes! The crabbing and oyster-tonging lore are woven into the very fiber of the story; they never have that tacked-on, "educational" feeling. The atmosphere of Rass is so lovingly described -- both its beauty and its discarded tin cans, the unique twists of speech, the cloistered, clannish population -- that later, when it's apparent that the island is slowly sinking into the Bay, we mourn as if it were our own.

There's also a wonderful mother, an exasperating grandmother who gives us some insight into the problems of living with the aged, and a subtly handled incident in which Wheeze becomes infatuated with a much older man. (He has hands like a Pond's ad.) Jacob Have I Loved may lack unity, in spots, but it is a book of intense flavor and color, and it adds an endearing character to the population of Katherine Paterson's private world.