PEOPLE slipped into the folding chairs gathered around the screen and stuck to them on that hot, humid night as faithfully as family members gather to watch slides from the latest vacation.The lights dimmed and in walked a tall, striking woman in a black pants suit, white blouse, and diffident smile. After she was introduced to the crowd who had come to hear her speak about her photographs, Annie Leibovitz ran a hand through her sun-streaked blond hair and asked the projectionist to start. Though she is known around the world for her work as photographer for Rolling Stone, Vanity Fair, and other publications, she chose to treat the fans assembled at the National Portrait Gallery for the op ening of her show like family, confiding in them the intimate stories behind her pictures of the famous. Actor and comedian John Cleese flashes on the screen, hanging upside down from a limb high up on a gnarled tree. How did she coax him into that precarious position? "He said he'd like to hang upside down from a goal post" for his photo, Ms. Leibovitz said. "And then I wondered whether we could find a great tree" instead. She did find a picturesque tree. But it was too dangerous for Cleese to hang from its high, rickety branch, so a little stabilizing magic was arranged. More pictures flicker by: actress Bette Midler, lying on a bed of red roses; singer Patti Smith, lit by burning kerosene kegs at night; singer-ecologist Sting, photographed in the buff, standing on one leg like a flamingo; novelist and polo player Jerzy Kosinski, shirtless in riding britches in a stable; a portrait of soccer champion Pele showing only his battered feet; and, of course, the famous photo of John Lennon with Yoko Ono taken two hours before his murder. Leibovitz is currently in the spotlight because of her recent controversial cover photo for Vanity Fair of a nude and pregnant Demi Moore, actress and wife of Bruce Willis. Leibovitz's career began in college, with an assignment to do a cover shot of Lennon for Rolling Stone. She was later assigned to photograph the Rolling Stones on tour. A shot of Mick Jagger looking rather dissolute popped on the screen, and Leibovitz said, "This is my Francis Bacon portrait of Jagger." Leibovitz had started out not as a photographer but as an art student at the San Francisco Art Institute, where her photos caught the eye of Rolling Stone's art director. Two years later, at 22, she became chief photographer for Rolling Stone. "Her portraits became the magazine's visual signature and dominated both the inside and cover. To be photographed by Leibovitz became the badge of honor to the counterculture" writes Willis Hartshorn in the catalog for the show, "Annie Leibovitz: Photographs 1970- 1990." Mr. Hartshorn is deputy director for programs of the International Center of Photography in New York, which organized this show along with the gallery. Leibovitz moved to Vanity Fair 13 years later, catching the spirit of the '80s as she had caught the '70s at Rolling Stone. According to a catalog essay, "As the preoccupation with money, power, status and success of the 1980s replaced the '60s enthusiasm for alternative lifestyles, Vanity Fair has provided Leibovitz with an expanded range of sitters, allowing her work to reflect the changing cultural climate. Through this work her portraits have made it from a base in the counterculture to more mainstre am public culture." William Stapp, the National Portrait Gallery's curator of photographs, describes her contribution as "a wit, that reflects her understanding of contemporary popular culture, an ability to achieve an intimate rapport with her subjects, and a visual audacity that is unusual in the history of portrait photography." He suggests that she comes from a tradition that includes Edward Steichen, Man Ray, Richard Avedon, Irving Penn, and Arnold Newman. Leibovitz is much more modest, suggesting that her memories of family snapshots, where everyone was constantly lined up and shot directly, had a big influence on her later work. She viewed her time at Rolling Stone as lab in which she could develop her journalism-rooted photos. It was at Vanity Fair that she began to develop a reputation as a startling, innovative portraitist. In shooting celebrities she became a celebrity herself and moved into the commercial world with her riveting photos for American Express advertising campaigns, The Gap, and other corporate clients. The show will tour in Europe when it closes at the National Portrait Gallery at the end of August.