BOOK REVIEW : Picking Up Where a Master Left Off : THE BUCCANEERS <i> by Edith Wharton</i> , <i> Completed by Marion Mainwaring</i> ; Viking, $22, 384 pages

What could be more tempting to a scholarly novelist than an unfinished book by an acknowledged master?

When Edith Wharton died in 1937, less than half of “The Buccaneers” was completed. Though a meticulous outline existed, the idea of enlisting a surrogate apparently didn’t occur to Wharton’s publishers, who issued the manuscript in its partial form. Even in that truncated edition, the book’s merits were impressive.

Now, Marion Mainwaring, a writer and translator who helped R.W.B. Lewis research his biography of Wharton, has completed “The Buccaneers.”

Like much of Wharton’s work, this novel examines the impact of new wealth upon an entrenched establishment, and interaction offering superb opportunities for the author’s particular brand of social satire.

The novel, which opens during the economic boom of the 1870s, centers on three brand-new American millionaire families: the St. Georges, whose wealth is subject to the vagaries of the stock market; the Ellsworths, whose fortune is a few months older and sturdier; and the Clossons, who have highly profitable and somewhat mysterious business interests in Brazil.

While the husbands are away enhancing the family holdings, the three wives are summering in Saratoga Springs, still an elegant resort but rapidly losing ground to Newport, where the truly fashionable have built their colossal “cottages.”

These ladies are worried. All the most eligible young men have been lured away to Rhode Island, and their beautiful daughters have been reduced to dancing with each other in the Saratoga Hotel Ballroom. If the suitor drain continues, the St. George, Ellsworth and Closson girls may find themselves withering on the vine before their 20th birthdays, supplanted by next year’s crop of debutantes.

Matters are aggravated by the fact that none of these families has been accepted into New York society, despite strenuous and costly attempts to breach the wall separating old money from new.

To improve her daughters’ chances in the matrimonial marketplace, Mrs. St. George engages an English governess, exquisite but shallow Virginia and her thoughtful and sensitive 16-year-old sister, Nan, who emerges as the real heroine of the story. Though 18 and 16 seem somewhat advanced ages at which to have a governess, apparently the 19th-Century idea of the job included chaperonage as well as advanced instruction in the airs and graces appropriate to one’s hoped-for place in society.

Miss Laura Testvalley, related to the Anglo-Italian Rossetti family and a woman of considerable intellectual attainments, more than fills the bill.

When further attempts to gain entrance into New York society founder, Miss Testvalley suggests that all of the girls spend a season in London, where her British connections may work the desired magic.

At that time, spirited and beautiful American girls were the toast of London, where their fortunes made them immensely attractive to the titled but impecunious (and sometimes wastrel) younger sons of dukes and earls. These particular American belles are an instant success. Guided and coached by Miss Testvalley, who not only engineers the necessary introductions, but provides the reader with a superbly ironic view of British manners and mores, the young American women soon find British husbands.

Once wedded to philanderers, fortune hunters and fools, they cope according to their personalities, divorce being entirely out of the question. Conchita Closson, the most daring of the group, finds extramarital solace, but the others soldier gallantly on, a testimonial to American family values.

Nan St. George, the endearing nominal heroine, becomes the duchess of Tintagel. She is married to one of the wealthiest and dullest men in the Empire, and she stoically endures her misery until she realizes that there is an escape, even if it means that she’ll never be presented at court again.

Marion Mainwaring, who picked up the strands of the plot where Wharton’s manuscript stopped, has finished the book in a style so close to Wharton’s in spirit, vocabulary, sentence structure and rhythm that the transition should be imperceptible even to the original author’s most ardent admirers.