As never before, girls are maturing earlier and have become so preoccupied with their bodies that they spend much of their energy managing and maintaining their looks at the expense of their creativity and mental and physical health, says a new book by an award-winning Cornell University historian.

"Girls today make the body into an all-consuming project in ways young women of the past did not," said Joan Jacobs Brumberg, professor of human development and of women's studies at Cornell and author of the new book, The Body Project: An Intimate History of American Girls (Random House, 1997).

The book chronicles how opportunities for self scrutiny have escalated during this century, with mirrors, movies and marketing raising young women's self-consciousness to excruciating levels.

"All this 'bad body fever' and preoccupation with physical perfection raise girls' liability to be exploited," says Brumberg, a Stephen J. Weiss Presidential Fellow and professor at Cornell. "Girls who want to be wanted so badly are unable to be critical about their sexual options and can be easily manipulated, coerced, even abused."

Brumberg explains how commercial interests play directly to the body angst of adolescent girls -- enormous revenues are at stake for manufacturers of skin, hair and diet products -- while popular culture and peer groups pilot contemporary teenage life.

"At the same time, traditional social supports for young women have disappeared, putting girls today in crisis and at much higher risk than boys for eating disorders, substance abuse, dropping out of school, depression and suicide," Brumberg says.

Brumberg warns: "Contemporary girls are in trouble . . . young women develop physically earlier than ever before, but within a society that does not protect or nurture them in ways that were once a hallmark of American life. . . . Contemporary girls seem to have more autonomy, but their freedom is laced with peril."

Sexual liberalism without a feminist base can have negative consequences for girls, said Brumberg in an invited address to the American Psychological Association in August -- an unusual invitation for a historian. Her analysis on the paradigm shift in girls' self perception from the l9th to 20th century, however, is of particular interest to American psychologists.

Brumberg calls for a new era of "girl advocacy" in which multigenerational dialogues on sexual ethics would better prepare girls in ways that go far deeper than the simple maxim, "Just say no."

As a social "intimate" history of girls, Brumberg draws heavily from girls' diaries over the past 100 years to glean insights into the hidden history of female adolescence. Integrating information from history, the history of medicine, human development and women's studies, Brumberg discusses topics -- using a social historical perspective -- ranging from menarche, sanitary napkins and tampons to the hymen, brassieres, pimples and body piercing. She seeks to better understand why girls today view "good looks" as the highest form of female perfection, unlike girls 100 years ago who strived for "good works."

Whereas girls of yesteryear believed that paying less attention to the self and more attention to helping others was important for self-improvement and personal identity, today's girls "are concerned with the shape and appearance of their bodies as a primary expression of their individual identity," Brumberg writes.

The author of the much-lauded book on the history of anorexia nervosa, Fasting Girls (Harvard University Press, 1988; New American Library Paperback, 1990), Brumberg has embarked on a major book tour in an effort to make her scholarly research in women's history, cultural history and human development accessible to a broad audience. For example, she will discuss The Body Project, which is written and intended for mothers, daughters, teachers, students, historians and others interested in the health and welfare of contemporary adolescent girls, on NBC's "Today Show" on Sept. 9 and is slated to be on National Public Radio's "Fresh Air" in early September.

Heavily illustrated with photographs to depict changing views of American womanhood over the decades, The Body Project traces the shifts in how girls think and feel about their bodies now that they menstruate and lose their virginity at much earlier ages than ever before and try to cope with a consumer and media-driven culture that "seduces them into thinking that the body and sexual expression are their most important projects."

The 250-page book begins with a review of the new biological timetable (in which menstruation occurs, on average, at 12 instead of 16, as it did 100 years ago) that governs the bodies of today's girls. Brumberg points out that girls today are likely to be sexually active before the age at which their great-great grandmothers had even begun to menstruate. She compares the Victorian view on menarche with today's and chronicles the diminishing mother-daughter dialogue, the disappearance of single-sex groupings and intergenerational mentoring and discusses how these trends endanger today's teen girls.

She shows how recent social trends have shifted discussions on puberty and menstruation away from mothers to doctors and the sanitary product industry who focus on hygiene rather than on fertility and how these trends exert "excruciating pressure on those body parts that the world can see."

Brumberg then presents a social history of acne, pointing out how skin care was the first of many different body investments made by middle-class parents to achieve a new ideal of physical perfection in their daughters; orthodontia, weight-loss camps, contact lenses and plastic surgery all followed. "American girls could not help but internalize this powerful imperative [for physical perfection] and, in the process, they developed their own, even more compelling, body projects," writes Brumberg.

She shows why contemporary girls have become so worried about their shape, size and muscle tone and discusses "breast buds," brassieres, figure control, dieting, clothes shopping, body piercing and genital piercing. "In a culture, where everything is 'up close and personal,' it should not surprise us that some young women today regard the entire body, even its most private parts, as a message board," Brumberg writes.

Such trends have led to sexual coercion of young girls, the demise of chastity as an ideal, the waning of virginity, the rise of sexually active girls throughout middle America and dwindling parental power. Although girls enjoy a new world of sexual freedom, Brumberg says, it is fraught with hazards since many girls are also victims of a century of change in sexual mores and behaviors.

Brumberg's research and writing on adolescent girls has received the support of the John Simon Guggenheim Foundation, the National Endowment for the Humanities and the Rockefeller Foundation.

EDITORS: For a review copy, contact Liz Fogarty at Random House at (212) 572-2693 or email efogarty@randomhouse.com.