WHEN, a couple of years ago, the movie Grease was re-released in the States, Olivia Newton John happily accepted an invitation to attend the glitzy Hollywood premiere. Somewhere in the back of her closet she found the black leather jacket and the skintight spandex pants she wore in the film. What the hell, she thought, it might be fun to wear them once again for old time's sake. As it turned out, the jacket fitted

perfectly. The problem was the pants.

The elastic had frayed beyond repair and, even if it hadn't, she still couldn't get them over her ankles.

It is fair to assume that, in the back of many a fortysomething woman's closet, there lies a pair of similarly frayed and long-forgotten skintight spandex pants. For in Grease Olivia was Sandy and Sandy was the role model for a generation of clean-cut ''All-American'' high school wanabees. Tell me more? Okay.

First released in 1978, Grease was the word and the word spelled instant success for Olivia Newton John. But, unlike her co-star John Travolta, her film fame was shortlived. Her movie career never really took off beyond the confines of Rydell High. Granted Travolta had his post-Grease lean times (it wasn't

really until Tarantino stepped in with Pulp Fiction 15 years later, that his movie star

status was finally confirmed) but Olivia never got past first base on the silver screen.

However, that may well be about to change. The singer is attempting to resurrect her acting career in a controversial new film called Sordid Lives, directed by American independent film-maker Mel Shores. Gone is the Miss Goody Two-Shoes image of Grease and in its place comes a raunchy, lived-in, old slapper called Bitsy Mae Harling. Bitsy Mae is your average Texas white trash bar-room singer - or, in other words, a tattooed, lesbian, ex-con with a drink problem. The transformation is remarkable.

And to think it all started with a little help from Cliff Richard and a Shadow. Olivia Newton John was born, a baby boomer, in Cambridge in 1948. Her grandfather was a Nobel Prize-winning scientist. When she was five, her parents emigrated to Australia. As a youngster she formed a schoolgirl vocal quartet and later, as a solo singer, she won a television talent contest sponsored by Johnny ''The Australian Elvis'' O'Keefe. The prize was a trip back to the United Kingdom.

Once in London, the teenage Olivia worked with Australian singer Pat O'Carroll as the somewhat unimaginatively-named Pat and Olivia duo. When O'Carroll was forced to return Down Under (his work permit ran out) she signed up to join a two-boy/two-girl vocal group called Tomorrow, manufactured by bubblegum king Don Krishner, the man behind the Monkees. When a planned TV series fell through, she left to pursue a solo career.

It was around this time that she met the Shadows' rhythm guitarist Bruce Welch who became, not only her producer, but also her fiance. There followed a string of saccharine-sweet, middle-of-the-road singles. She should, were there any justice, have been hauled up in court and charged with murdering Bob Dylan's If Not For You and George Harrison's What Is Life. The lesser charge of GBH would have been filed against her for her version of John Denver's Take Me Home Country Roads and the equally tortuous Banks of the Ohio. Still, one should never over-estimate the record-buying public's taste. All of the aforementioned songs were major hits.

Through Welch, with whom she eventually split, Newton John was introduced to Cliff Richard, pop's paragon of virtue. A friendship ensued (though, as ever with Cliff and the ladies, it remained purely platonic) and she became a regular guest on his BBC Saturday night shows during the early seventies.

By now, however, she had made a significant - and, to many, a surprising - breakthrough into the American market. In 1975 she won a Grammy for Best Country Vocalist, and the following year her Best Female Vocalist prize at the Country Music Awards prompted several resignations from the C&W purist stetsons in Nashville.

Meanwhile, back in Britain, her career had taken a slight turn for the worse. She had represented the UK in the 1974 Eurovision Song Contest. Unfortunately, it was the same year as Sweden entered a group called Abba. Olivia had met her Waterloo. So she headed west across the Atlantic and settled in California.

And there, quietly and comfortably obscure, she might have stayed had she not one evening attended a dinner party in Los Angeles. Across the table from her was film producer Allan Carr who was in the throes of planning a big screen musical about a bunch of fifties high-school teenagers. He'd found his male lead - a minor TV star called Travolta who had just finished work on his first movie, the as yet unreleased Saturday Night Fever - but he was struggling to find a female lead. What he needed was a pretty young woman who could sing, dance, and (here's the tricky part) who could play both the virgin and the vamp in the same character. Somewhere between the peanuts and the pudding, he offered the role to Newton John.

She later recalled: ''I was a little nervous at first. I actually asked if I could do a screen test. After all, I was 29 and would be playing a 17-year-old so I wanted to make sure I could pull it off.''

She did. Grease was and remains the most successful movie musical of all time. Olivia's schizophrenic performance - one minute she's the goody-goody Sandy, the next she's the hardhat-permed, lycra-wearing, heavy-duty make-up, sexpot Sandy - touched all the right buttons in the teenage target audience.

Though it did no great shakes for her movie career, Grease paved the way for Newton John to shed her sugar-sweet persona and adopt a raunchier image, perhaps best exemplified in her 1981 album and single Physical, in the video for which she successfully combined aerobics and sex appeal. By 1985 she was a million miles away from the banks of the Ohio, posing half-topless with a riding crop in Helmut Newton's photo for the cover of Soul Kiss. It was the kind of transformation which, when you think about it, fellow Aussie chanteuse Kylie Minogue achieved in almost carbon-copy style a generation later.

These days, Olivia Newton John is hopelessly devoted to taking every day as it comes - and thanking God for each of them. For misfortune and tragedy have often been cruel companions to her over the years.

There was her failed marriage to dancer and bit-part actor Matt Lattanzi, 11 years her junior. Then there was her financial ties to Koala Blue, an LA-based, Aussie surf-styled, sportswear company which she launched in 1982. For the best part of 10 years, the company seemed successful, building up to an annual turnover of $14m and with 49 outlets on four continents. Then in 1991 the firm suddenly filed for bankruptcy. She blamed the economic recession. Others blamed poor management, undependable deliveries, and shoddy merchandise. The truth probably lay somewhere in between.

But these problems paled into significance compared to what happened next. First, in 1991, her beloved five-year-old goddaughter died of a rare childhood cancer. Then the following year her father, Brinley, 78, an Australian-based professor of German literature, succumbed to liver cancer.

And then, worst of all, just two weeks after her father's death, doctors diagnosed Olivia with a malignant tumour in her right breast. ''It was all at once,'' she would recall. ''Everything just came at me. You can't help but feel despair at some point. It was overwhelming.''

But she did not give in. A radical mastectomy and a saline implant followed. Then came the months of painful chemotherapy. Through it all, she relied on laughter to maintain her balance. ''She had a sense of humour even when they were putting the needle in her vein,'' said her older sister, Rona. To cope with the side-effects she relied on herbs, acupuncture, and mental imaging. It was California, after all.

Nowadays she talks about her cancer in the past tense. It's gone, she has survived. She doesn't even use the word ''remission'' because that makes it sound as if it's lurking round a corner, waiting to return.

So Olivia Newton John is alive and well and living in Malibu. With her are three cats, three dogs, and two cockateils. With her, too, are her long-term partner, film cameraman Patrick McDermott, and 15-year-old Chloe, her daughter from her first marriage.

She is a tireless worker on behalf of cancer awareness. She serves as national spokesperson for the US Children's Health Environment Coalition, a non-profit-

making organisation dedicated to researching links between childhood cancer and exposure to carcinogenics. She was also for three years a goodwill ambassador for the United Nations.