After many decades of fighting for equality, women have never had it so good. They run corporations, lead universities and pilot fighter jets - and soon a woman named Hillary may be sworn in as president of the United States.

But despite this progress, a leading academic says that today's girls are being told that the secret formula to getting ahead in the world is simple - to look and act 'sexy'.

In her new book Prude: How the Sex-Obsessed Culture Damages Girls, American lawyer Carol Platt Liebau says that the modern trend towards overt carnality is undermining girls' sense of worth in their most vulnerable formative years and rewarding destructive behaviour.

Once upon a time 'slut' was one of the greatest insults a teenage girl or woman could face. But now being labelled a 'prude' is deemed to be even worse, says Liebau.

"The overwhelming lesson teenagers are now learning from the world around them is that being 'sexy' is the ultimate accolade, trumping intelligence, character and all other accomplishments at every stage of a woman's life," says Liebau, who made history by becoming the first female editor of the distinguished Harvard Law Review.

"The new female imperative is that it is only through promiscuity and sexual aggression that girls can achieve admiration and recognition."

In a tabloid world dominated by the 'bad girl' antics of Paris Hilton and Britney Spears, Liebau says that young girls are being brainwashed into believing good looks, promiscuity and a lavish lifestyle are synonymous with success.

"In a culture that celebrates Paris Hilton, thong underwear and songs like My Humps - where the female singer Fergie expounds the sexual magnetism of her breasts and buttocks - there's scant recognition or respect for female modesty or achievement that isn't coupled with sex appeal," she says.

With televised images of overtly sexualised women and magazine articles celebrating Hollywood 'It girls' as role models, young women are learning that to get ahead in life they need to "just do it", according to Liebau.

The obsessive scrutiny of celebrities and fashion models has also placed young women under intense pressure to look "bone slim". "Living in an overly sexualised culture takes a toll on girls," she says.

Movies such as Mean Girls, Cruel Intentions and the music of Britney Spears, Christina Aguilera and the Pussycat Dolls are all cited by Liebau as endorsing sexiness as the ultimate accolade - while diminishing intelligence, integrity and humility.

"Girls are being led to believe they're in control when it comes to sexual relationships," she says. "But they're actually living in a profoundly anti-feminist landscape where girls compete for attention on the basis of how much they are sexually willing to do for the boys.

" Earlier this year, a new report by the American Psychological Association blamed mainstream American culture - particularly the media - for depicting women in a sexual light and warned that such images may make young girls think of their own bodies as sexual objects.

"Throughout US culture, and particularly in mainstream media, women and girls are depicted in a sexualising manner," said the report, which linked the sexualisation of girls to eating disorders, depression and low self-esteem later in life.

The researchers looked at advertising showing body-baring doll clothes for pre-schoolers, 'tween' girls posing in suggestive ways and the sexualised antics of young Hollywood A-listers.

The emergence of the 'tween' market - a multibillion-dollar industry of clothing, toys and cosmetics aimed at the vulnerable seven to 12 age group - has helped sexualise young girls barely young enough to understand the sassy messaging in the clothes they wear.

With padded bras for flat-chested pubescent girls, electronic 'make-over' games for six-year-old girls and thong underwear for seven-year-olds, bearing the logos 'Wink Wink' or 'Eye Candy', anything goes for 'tweenagers' desperate to emulate their celebrity heroines.

Last year, Tesco in the UK came under fire for selling a 'Peekaboo' pole-dancing kit which offered to 'unleash the sex kitten within'.

Although the company protested the kit was marked for adult use, it was displayed for sale on the toy and games section of its website.

WH Smith reported that its Playboy stationery for schoolgirls - emblazoned with the pink bunny logo of the Hefner soft-porn empire - has been one of its best selling items ever.

"Even young girls are the willing, active and conscious participants in a tawdry, tarty, cartoon-like version of female sexuality," says Ariel Levy, author of Female Chauvinist Pigs, a book that examines how popular culture has embraced a model of female sexuality originating from pornography and strip clubs.

When it comes to when they should engage in sexual activity, Liebau argues that young women are taught to deal with this momentous decision in just the same way they would deal with a shopping mall purchase. Whether or not to have sex is presented as just another choice, much like whether to purchase a Britney Spears album or one by Christina Aguilera," she says. Liebau quotes actress Sharon Stone as one example of how "good" advice to girls can often turn bad.

Stone encourages teenagers who feel pressured to have sex to offer oral sex instead. "Young people talk to me about what to do if they're being pressed for sex. I tell them what I believe ... if you're in a situation where you cannot get out of sex, offer a blow job. I'm not embarrassed to tell them," Stone says.

"Perhaps," Liebau notes wryly, "she should be."