Helen Hooven Santmyer, a retired college dean and research librarian whose 50-year-long literary effort " . . . And Ladies of the Club" became a surprise best seller in 1984 when she was 88, died yesterday at the nursing home in Xenia, Ohio, where she had lived for five years.

Miss Santmyer, 90, died in her sleep, according to nursing supervisor Sylvia Rosenlieb of the Hospitality Home East.

The book, begun in the late 1920s as Miss Santmyer's reaction to Sinclair Lewis' novel about small-town life, "Main Street," was scrawled in longhand in bookkeepers' ledgers over the next five decades. When finished, "Ladies" filled 11 boxes, rivaling Margaret Mitchell's first draft of "Gone With the Wind" in sheer bulk. The printed book ran 1,176 pages and has sold nearly 370,000 copies in hardback.

The novel, Miss Santmyer's third, was first published in 1982 by the Ohio State University Press and sold only a few hundred copies. But it was catapulted to national attention after Grace Sindell, of Shaker Heights, Ohio, overheard a librarian recommend it. Sindell, in turn, recommended it to her son, who told an agent about the book. The agent contacted G.P. Putnam's Sons, which published it in 1983.

Within weeks, "Ladies" was the number one best seller on the New York Times list and the main selection of the Book of the Month Club.

By then, Miss Santmyer lived in a nursing home, was nearly blind and suffered from emphysema. She took celebrity at her own pace: a small sign at the nursing home told autograph seekers to check first with the nurse at the front desk.

"It may have taken me 50 years to get it done," she said later, "but I didn't do it all at once. I had a living to make . . . . Whatever the job was it had to come first, of course."

Spanning the years from immediately after the Civil War to the Depression, "Ladies" traces the lives of two families in the thinly fictionalized Ohio town of Waynesboro -- actually Xenia -- through the meetings of a ladies' literary club.

Each chapter, which generally covered a year or more, used the device of the club's membership rolls to chronicle the comings and goings, marriages and deaths of the townspeople. The descriptions, however, were not limited to small-town happenings, but were filled with treatises on Republican Party politics and the effects of Reconstruction, the Industrial Revolution and the Depression on the Midwest.

A native of Xenia, Miss Santmyer attended Wellesley College, worked in New York as a secretary to the editor of Scribner's magazine, and earned a bachelor of letters degree at Oxford University.

Miss Santmyer, who never married, returned to Xenia in 1929, and later served as dean of women and head of the English department at Cedarville College in Ohio. She also was a reference librarian in Dayton.

In the 1920s, she wrote two novels, "Herbs and Apples" and "The Fierce Dispute." A book of Miss Santmyer's reminiscences, "Ohio Town," was published by the Ohio State University Press in 1963.

She is survived by a niece.