Chanting "Harry Potter rules!" and holding up signs proclaiming "Potter Power," pupils at the Montclair Kimberley Academy greeted J. K. Rowling, the author of the wildly popular Harry Potter children's books that have dominated best-seller lists nationwide for much of the year.

Yesterday's reading, book-signing and question-and-answer session in Montclair was the only school stop on the 33-year-old British author's North American publicity tour for her new book, "Harry Potter and the Prisoner of Azkaban," the third novel in the series that is currently No. 1 on the USA Today best-selling fiction lists.

The three books of the series now rank numbers 1, 2 and 3 on both the Wall Street Journal list and New York Times list, where the first book, "Harry Potter and the Sorcerer's Stone," has spent 42 weeks.

Rowling's choice of the private school caused a few pupils to wonder if Rowling - who sent her magical hero, Harry Potter, to a school for witchcraft and wizardry - "knows something about the academy that we don't," said fifth-grader Caroline Richardson, 10, of Upper Montclair.

''Actually, she chose to come here because the children of one of her editors attend Montclair Kimberley," said Debbie Kozak, a spokeswoman for the school. Kozak also cited the school's large book fair, which will begin Nov. 6, and its history of inviting children's authors to speak there as reasons that convinced the reclusive author to visit the school.

Three pupils from each of Montclair's other private and public schools and St. Philip's Academy in Newark were also invited to attend. They received signed copies of the author's three books for their school libraries.

Rowling was greeted with a standing ovation before reading from page 26 of "Harry Potter and the Sorcerer's Stone," a selection that describes a Harry Potter who is not yet aware of his magical powers.

Answering questions prepared by children from various grades, Rowling revealed that on "good days" she writes at least nine hours a day, breaking only for lunch and to care for her daughter at dinner time. Writer's block only bothered her once, Rowling revealed, after her "Harry Potter and the Chamber of Secrets" came out.

''Suddenly, I was getting a lot of attention in the press, and I panicked," she told the audience. "I felt like my writing was no longer my private world. It was like somebody was looking over my shoulder and saying, 'Well, that's not a very good word, is it?' After a few weeks, it went away."

As for favorite authors, Rowling said she admires Jane Austen, C.S. Lewis and Paul Gallico. But asked what "classic" children's books she read in her youth, Rowling took exception with the word "classic" and replied, "James Bond. I was really very lucky growing up - my parents let me read anything and everything. Adult books. The works."

Reading, for Rowling, is an active pastime. "You have to work with the author and make what he's describing happen in your head," she said. "You cast and direct the film in your mind, and nobody but you sees what you see. That's why reading is irreplaceable."

Asked if she ever thought her books would become so popular, Rowling said, "No, not really. Apart from the birth of my daughter, the happiest day of my life was when I got the letter telling me that a publisher had actually accepted my novel. I never dreamed it would be such a success."

Fran Kurtis, who teaches second grade at Montclair Kimberley, knows why children love the character of Harry Potter, an eleven-year-old who was orphaned as an infant and grows to discover he is a wizard born of wizard parents. "They're the archetype of the children's novel," said Kurtis, " 'foundling' stories with an abandoned child triumphing over evil with the help of benevolent others and special powers."

Schoolyard reviews for Rowling's new novel are also positive.

''I've read all three books," said Liz Kneuer, 10, a fifth-grader from Upper Montclair, "and I like 'The Prisoner' best because it's not just a continuation of the other books. You don't know what's going to happen next, or who the good or bad guys are."

Armando Tamargo, 7, a second-grader from Montclair has another take on the Harry Potter books. "I like them because they're very interesting and long. I can make my parents read all night long."