ublishers usually aren't happy when a competitor's book hits the best-seller list. But the success of "The Da Vinci Code" by Dan Brown, a murder mystery by a little-known writer that made its debut at No. 1 on The New York Times best-seller list, has caught the attention of an industry mired in a dismal retail economy.

Normally jealous rivals have been relieved to see that an aggressive marketing campaign and enthusiasm among booksellers can fuel sales, particularly for newer writers.

The novel, Mr. Brown's fourth, has as its protagonist Robert Langdon, a Harvard professor of symbology who investigates a murder at the Louvre. The novel sold more copies in its first two days, about 8,000, than any of Mr. Brown's previous books had ever sold in hardcover. There are 354,000 copies in print.

New books by authors like John Grisham, whom Mr. Brown displaced at the top of the list, often hit No. 1 right away. But it is unheard of for a writer without a track record of success. "The Da Vinci Code" was No. 1 on the Times list for two weeks, before it was displaced this week by "Birthright," by Nora Roberts. Mr. Brown's success seems to many to herald the birth of a brand-name novelist.

"That Doubleday was able to make this book No. 1 in its first week on sale gives us something to talk about in the industry ó and try to duplicate," said Michael E. Morrison, publisher of the Morrow/Avon division of HarperCollins, the publishing division of the News Corporation. "It gives renewed hope that it is possible to reach more customers willing to take a chance on an unknown author. In the 80's and 90's it seemed easier to break out new fiction writers."

Mr. Brown has produced the kind of cash register ring that the book business needs. Sales at Barnes & Noble stores open at least a year fell 8.4 percent in March, a precipitous decline, according to a company statement announcing a first-quarter shortfall. Borders, the second-largest book retailer, said it would post a loss when first-quarter results are released next month.

"The Da Vinci Code" is Mr. Brown's second book with Robert Langdon as its central character. The first, "Angels and Demons," was published in 2000 by Pocket Books, which also published "Deception Point," a novel outside the Langdon series. When Mr. Brown's editor, Jason Kaufman, moved to Doubleday in 2001, "The Da Vinci Code" was his first acquisition.

Doubleday paid close to $500,000 for two books, nearly five times the $100,000 Pocket paid for its two books.

Mr. Brown, a former English teacher at Phillips Exeter Academy in New Hampshire, is a practitioner of what might be called the encyclopedia school of popular fiction perfected by authors like Arthur Hailey and Patricia Cornwell, who mix potboiler plots with arcane facts about the hotel industry or forensic medicine. In "The Da Vinci Code," clues to the murder are to be found in Leonardo da Vinci paintings, leading Langdon and his sidekick, the cryptologist Sophie Neveu, to members of Opus Dei and other secret societies.

"John Grisham teaches you about torts," said Stephen Rubin, president and publisher of the Doubleday Broadway publishing group. "Tom Clancy teaches you about military technology. Dan Brown gives you a crash course in art history and the Catholic Church."

When 100 pages of Mr. Brown's manuscript were circulated to the company's sales force last summer, the enthusiasm confirmed Mr. Rubin's optimism. "There was a unanimous `Oh my God' response," Mr. Rubin remembered. "If people internally are responding unanimously and rhapsodically, there's no reason to think people externally won't react the same way."

Doubleday sent 5,000 advance reader's editions to booksellers and the news media in early fall and another 5,000 copies in January. The total number, 10,000, is larger than the first printing of most books and more than any of Mr. Brown's books had sold. Little, Brown distributed 3,900 advance copies of of Alice Sebold's "Lovely Bones," another novel by a largely unknown writer that became a surprise No. 1 on the best-seller list last year. That was also an exceptionally large amount.

Doubleday sent Mr. Brown on an extensive prepublication publicity tour to meet booksellers, rare for an author without a marquee name. He attended a dinner with Borders management, and went to Barnes & Noble's annual managers meeting. Antoinette Ercolano, the chain's vice president for merchandising, told the assembled managers of the chain's 900 individual Barnes & Noble and B. Dalton stores that the novel was the first book she had read in a long time that "kept her up at night," said Sessalee Hensley, the chain's fiction buyer.

Tamara L. Heim, president of Borders stores, sent a letter about the book to the chain's store managers, an unusual move. On the Barnes & Noble intranet, store staff members posed with the book and told why they liked it, the first time the Web site was used to do more than display the titles and jackets of notable books.

To meet independent booksellers, Mr. Brown also went to regional conventions through the fall and winter.

The success is all the more remarkable because Mr. Brown's first three books sold poorly. "Everyone gets stuck on the idea that a track record is the future," said Emily Bestler, editorial director of Pocket Books at the time it published Mr. Brown. "It does take time for an author to build. We hear that you cannot take big steps, but he did it."