As befits the best-known student at the Hogwarts School of Witchcraft and Wizardry, Harry Potter has achieved much magic during his brief literary life. But his latest improbable feat may be the greatest: Harry's newest adventure has become the No. 1 bestseller at one of America's biggest book outlets--nearly two months before it goes on sale.

Everyone in the book business knew that the new novel, "Harry Potter and the Prisoner of Azkaban," to be published by Scholastic on Sept. 8, was going to be a blockbuster. But nobody knew it would happen this fast. Word of mouth for the third tale in the funny and inventive series by the British author J.K. Rowling has been so strong among preteens--and their parents--that the book now ranks as the top-selling title on the bestseller list at Amazon.com, the revolutionary Internet bookstore.

"We don't know of any other title that made it to No. 1 on pre-orders this far ahead of publication," said Amazon's Lizzie Allen. "Nobody matches the demand for Harry."

So powerful is Harry's magic that Scholastic plans a first printing of 650,000 copies. That total would seem wildly excessive for a British schoolboy story, if it weren't for the astronomical American sales of the two previous Potter books.

The first adventure, "Harry Potter and the Philosopher's Stone," was published in the United States just 10 months ago under the title "Harry Potter and the Sorcerer's Stone" and has sold about 800,000 copies.

The sequel, "Harry Potter and the Chamber of Secrets," has done even better, with 900,000 copies in print since its publication on June 2, the publisher says. That's a higher rate of sale than the best-selling American novel of 1998, John Grisham's "The Street Lawyer." That book came out in February 1998 and sold 2.55 million copies that year, according to Publishers Weekly.

The secret to Harry Potter's appeal is that J.K. Rowling is a marvelous storyteller.

Her funny, suspenseful and surprising tales relate the history of an orphan with a mysterious lightning-shaped scar on his forehead. At age 11, Harry Potter wins a scholarship to Hogwarts, "the world's greatest school of wizardry," where he begins to learn the truth of his fantastic ancestry. His experiences resonate with children and former children alike: the neighborhood bully, the scary teacher, the lost pet, the agony of being the last kid picked for the team.

Rowling's world also has its unfamiliar elements. The most popular sport at Hogwarts School is Quidditch, which is like soccer, except that there are four balls and no player is allowed to touch the ground. The required school uniform is a black robe, a black pointed hat, and "one pair of protective gloves (dragon hide or similar)."

J.K. Rowling has little to say, though, about herself. Declining interviews, she acknowledges only that she is a single mother who started the first Harry Potter book to fill time on a stalled train. Several publishers rejected the manuscript before Bloomsbury decided in 1997 to take a flyer. Almost completely by word of mouth, the Potter stories have become the best-selling children's series here since "Peter Pan."

Rowling is working on the fourth Harry Porter novel now and plans seven in all. Warner Bros. has bought the film rights.

The third Harry Potter book has already been published in Britain--with explosive results.

On July 8, Thomas Harris's "Hannibal" was by far the best-selling book in this country. Then, on July 9, the new Harry Potter came out--and ate Hannibal for lunch. "Hannibal" sold an impressive 13,000 copies here during the second week in July. "Prisoner of Azkaban" sold 68,000 copies the same week.

Bloomsbury, the British publishers, played adroitly to Harry's youthful following by refusing to allow sales of the book before 3:45 p.m. on its publication day--theoretically, to stop Harry's fans from playing hooky.

The plan worked so well that bookstores the length of Britain were jammed with young readers, still in their school uniforms, when the magic moment arrived. The youthful buyers counted down the final seconds--"Three! Two! One!"--and many simply flopped on the floor and started reading the instant they got the book in their hands.

American kids will have to wait until September to get their hands on "Prisoner of Azkaban," and it is clear that many of them are impatient. "There hasn't been that much in the media, but readers are way ahead of the media on this one," says Scholastic's Kris Moran. "The kids and their parents just want this book."

Amazon's Current Bestsellers

1. Harry Potter and the Prisoner

of Azkaban by J.K. Rowling

2. Harry Potter and the

Sorcerer's Stone by J.K.

Rowling

3. Harry Potter and the Chamber

of Secrets by J.K. Rowling

4.Black Notice by Patricia

Cornwell

5. Body for Life: 12 Weeks to

Mental and Physical Fitness Forever by Bill Phillips, Michael D'Orso

6. The J.F.K. Jr. Scrapbook by

Stephen J. Spignesi

7. Why We Buy: The Science of

Shopping by Paco Underhill

8. Hannibal by Thomas Harris

9. Assassins (Left Behind) by Jerry

B. Jenkins, Tim F. Lahaye

10. Memoirs of a Geisha: A Novel by

Arthur S. Golden

CAPTION: J.K. Rowling enchants children and older readers with her three Harry Potter novels. The Briton plans to write seven in all.