HERE'S a statistic that tells a lot about the contemporary publishing business. In August, the Canadian company Harlequin Books will publish title No. 1,000 in its series called Harlequin Presents. The material in Harlequin Presents, a line dating back to 1973, is somewhat hotter than that contained in the sqeaky-clean Harlequin Romances. Sex must occur in the Harlequin Presents series, but with no explicit descriptions.

After it was launched, Harlequin Presents quickly became the best-selling brand-name series about contemporary romance in the world. The line is now published in 17 languages in over 100 countries. Eight titles are issued every month and sales of the average book are 300,000 or more in the United States alone. Harlequin is chary about giving national or worldwide sales figures on any given title. However, it does say that worldwide sales last year for the six imprints of Harlequin Books and the five issued by its companion romance publisher, Silhouette, were more than 250 million. Harlequin and Silhouette send forth a total of 58 books every month.

Most books in the Harlequin Presents series are written by a small coterie of authors. Charlotte Lamb and Anne Mather each have produced more than a hundred titles. The most famous author to come out of Harlequin Presents is Janet Dailey, who wrote 54 books in the line before moving on to become a best seller superstar elsewhere. Penny Jordan, author of title No. 1,000 -- Passionate Relationship -- has done more than 60 books in Harlequin Presents.

You can always tell a Harlequin Presents from the look of the cover. The background is white and the typeface is scroll-style. There is an oval picture depicting the principal characters in a clinch. Indeed, in Harlequin and Silhouette books, the trained eye can always tell from that cover picture what happens inside. For example, the Harlequin Temptation series, launched in 1984 to meet the demand for even steamier romance, has more explicit covers than Harlequin Presents. Shield your eyes.

News from Knopf

EARLIER this year, Robert Gottlieb left his job as president and editor-in-chief of the prestigious publishing firm of Alfred A. Knopf to become editor of The New Yorker magazine. To replace Gottlieb, Knopf imported a leading light of London publishing, Sonny Mehta. Now, in his first major personnel move, Mehta has hired one of the heaviest hitters among contemporary editors, Elisabeth Sifton. A vice president of Viking Penguin Books, Sifton has been editor of her own imprint there, called, appropriately enough, Elisabeth Sifton Books. Earlier this year, the imprint won the prestigious Carey-Thomas Award given by Publishers Weekly magazine for creative publishing. At Knopf, Sifton will be executive vice president.

She began work at the Viking Press in December 1968 and was editor-in-chief of the company from 1979 to 1983 before getting her own imprint. Among the writers she has worked with are William Gaddis, Robertson Davies, Don DeLillo, Peter Matthiessen, Geoffrey Wolff, John Ashbery and Victor Navasky. It is known that a number of writers have personal contracts with Sifton which specify that she will be their editor, so some may follow her to Knopf.

At Knopf, all is happiness. "This is wonderful news for all of us at Knopf," said Mehta. "Elisabeth is someone I have known and admired for many years. She is an outstanding publisher and a remarkable editor whose unique talents have long been acknowledged by everyone in the industry."

Dreiser Volume

THE LIBRARY of America, the great collection of our country's best writers, has just issued what will be the first volume of several devoted to the works of Theodore Dreiser. It is the 36th book in the Library of America series. Included are Dreiser's earliest novels -- Sister Carrie and Jennie Gerhardt -- and a collection of biographical sketches called Twelve Men.

Born in 1871, Dreiser was one of 10 children in a poor German-Catholic family. Influenced by the writings of Charles Darwin and Herbert Spencer and in revolt against his strict upbringing, Dreiser described in his books the gap between society's moral preachments and its gross materialism. He is sympathetic to characters caught in the grip of social forces.

Sister Carrie (1900), based in part on Dreiser's recollections of an older sister, tells the story of an innocent country girl who loses her virtue in the big city. But she rises in the world at the same time as her lover is driven to despair and suicide. The book differed radically from others of the time in that Carrie is not punished for her transgressions and does not feel guilty about them. Frank Norris, then an editor at Doubleday, Page accepted the manuscript. Frank N. Doubleday, horrified at the novel's supposed immorality, tried to break the contract and finally printed only 1,000 cheaply bound copies with no advertising. Only 450 were sold and the novel's reception almost drove Dreiser to suicide.

Jennie Gerhardt (1911) is loosely modeled on another of Dreiser's sisters. It tells of a poor German-American girl who becomes the mistress of a senator and then of a wealthy businessman. H.L. Mencken called it "the best American novel I have ever read, with the lonesome but Himalayan exception of Huckleberry Finn." It was much more successful than Sister Carrie, selling 13,000 copies in its first year. Twelve Men (1919) is a mix of journalism, autobiography and fiction. The sketches describe encounters with men Dreiser knew during his years as a journalist in the Midwest and New York City in the 1880s and 1890s. Included among the portraits is one of Dreiser's brother, Paul Dreiser, a popular songwriter whose works include "On the Banks of the Wabash."

The 37th volume in the Library of America will be a volume of Benjamin Franklin's writings, which will be published on Constitution Day, Sept. 17.

Schocken Books Sold

THE RESPECTED small New York publishing house, Schocken Books, has been sold to Random House, and will become a part of Pantheon, a Random House subsidiary. The Schocken name will continue and David Rome, president of Schocken and grandson of its founder, will be a consultant and advisory editor with Pantheon. The first Schocken list under the Pantheon aegis will be published in the spring of 1988.

Schocken was founded in 1942 by Salman Schocken, a refugee from Germany. It gained renown for issuing the collected works of Franz Kafka, and also published Martin Buber, Elie Wiesel and S.Y. Agnon. More recently, it had a best seller with When Bad Things Happen to Good People by Rabbi Harold S. Kushner.

Pantheon Books, of which Schocken is now a part, was also founded in 1942 by refugees from Germany, Kurt and Helen Wolff, who teamed with an American partner, Kyrill Schabert.

In the Margin

GREGORY ORFALEA, a Washington resident and editor of the Small Business Administration's newspaper, Network, has been named one of three winners of the Ithaca House Series national poetry competition. His manuscript, The Capital of Solitude, will be published in the poetry series of Ithaca House Press of Greenfield, N.Y. A second winner was Julia Wendell, editor of the Galileo Press in Sparks, Maryland, for An Otherwise Perfect History.

The Center for the Book in the Library of Congress has won the 1987 International Book Award, presented each year by the International Book Committee, a consultative committee to UNESCO. The group cited the Center for the Book for developing "an imaginative and practical campaign on behalf of books and reading" that has been imitated in many other countries. John Y. Cole, director of the center, will receive the award in London on Aug. 20.

John Huston has announced that his next film project will be an adaptation of Theophilus North, Thornton Wilder's novel about the rich of Newport, R.I. in the 1920s. The film will star the director's daughter, Anjelica Huston, who won an Academy Award for her role in the movie Prizzi's Honor. The New York firm of Carroll & Graf has recently published a new paperback edition of the novel.

The theme chosen for this year's National Children's Book Week (Nov. 16-22) is "Change Your Mind." A variety of posters and streamers underlining the theme are available from the sponsor, the Children's Book Council, 67 Irving Place, New York, N.Y. 10003. ::