Marilyn Monroe and Grace Kelly are twin idols of the American imagination. They defined between them the range and shape of desire in the 1950s.

More than six decades later, their power as enduring cultural icons has grown so strong we continue to obsess over their lives and careers, their loves and their fears.

So it's no surprise that Lifetime, cable TV's dedicated chronicler of the typical woman's wants and dreams, would pay homage to these women with a pair of new biopics.

Kelly is memorialized in the star-studded big-budget European production Grace of Monaco (9 p.m. Monday) with Nicole Kidman in the title role. And Monroe in the two-part mini-series The Secret Life of Marilyn Monroe (8 p.m. Saturday and next Sunday), an adaptation of J. Randy Taraborrelli's best-selling biography featuring Pan Am star Kelli Garner as Monroe.

Both pics are dreadful, badly written, and badly produced - infamously so in the case of Grace of Monaco, which crashed like a burning zeppelin at last year's Cannes Film Festival.

Despite their relative lack of aesthetic merit, these pictures are fascinating cultural documents. Though less than compelling in their portrayal of these two celebrities in their own right, they reveal a great deal about our apparent compulsive need to rehash and repeat the details of those lives.

We adore both of these women who managed to make, in careers that were both quite brief, a series of brilliant classics such as such as Rear Window and The Seven Year Itch. We watch these films again and again in part because they are great, but also to see how each carries her beauty, her unique sex appeal.

Though to be sure, most would take sides, preferring one or the other. (As Philadelphians, we are drawn, of course, to the East Falls girl, Kelly.)

Grace of Monaco was directed by renowned La Vie en Rose helmer Olivier Dahan. It's lush, rich in detail, and teeming with extras. It's the kind of film that's made with a view to the Academy Awards.

It's 1962, six years after Kelly wed Rainier III, Prince of Monaco (Tim Roth). She's borne him two children, yet she's unhappy, lonely, and considering an offer from her old friend Alfred Hitchcock to return to Hollywood to star in one of his pictures, Marnie, in a role that eventually went to Hitchcock's latest obsession, Tippi Hedren.

The story plays out against a political crisis: France threatens to annex its protectorate, Monaco, the tiny principality ruled by Rainier and Grace.

While still in preproduction, the film drew criticism from Kelly's son, Prince Albert, who denounced it as historically inaccurate fantasy. It continued to make headlines when a feud broke out over the film's tone between studio chief Harvey Weinstein on one side and director Dahan and producer Pierre-Ange Le Pogam on the other. Weinstein reportedly wanted a light tone, and the filmmakers were intent on producing a serious morality tale.

Scheduled to be released in American theaters in November, the film was pulled from theatrical distribution by Weinstein. That's when Lifetime acquired it - one imagines for a song.

The resulting film is a mess. Driven by a weak, facile screenplay, the film is singularly shallow in both intellectual and emotional content. Its structure is a mess: Fragmented and episodic, it simply doesn't cohere. (These problems are most likely exacerbated in the Lifetime version, which was cut by 20 minutes.)

Kidman seemed a natural choice to play Kelly. She manages to soar in several scenes. Hampered by the subpar material, she seems utterly lost, unable to master what could have been the role of her career.  

The Secret Life of Marilyn Monroe is far more watchable, due to a fine turn by Garner and author Taraborrelli's unique approach, which focuses on an aspect of Monroe's life usually ignored: Her complex relationship with her mother, Gladys (Susan Sarandon). A paranoid schizophrenic in and out of hospitals, Gladys lived with Monroe throughout the actor's career. But theirs was a secret relationship: To protect Monroe's image and privacy, the studios told the public both of her parents were dead.

Secret Life, set after the release of Monroe's last feature, The Misfits (1961), boasts an impressive cast, including Emily Watson, Embeth Davidtz, and Jeffrey Dean Morgan. But it's little more than a fragmented series of sketches stitched together by an ineffectual structure.

 The film is made with minimum attention to any of the details that bring a period film to life; each flashback reads less like a dramatic scene than a lifeless illustration.

Monroe and Kelly have such diametrically opposed images. We speak of images; reality is of no real concern when it comes to these films.

Monroe is the sexpot.

She blew hot, blew kisses, held her dress down against the rising tide of passion catching fire all around her.

Kelly ran cool. The daughter of a successful self-made businessman, she embodied the mystique of good breeding and classical beauty. She seemed to float above the leers the other incited with such facility. With a smile as sweet as a child's and yet as ironic and knowing as an Oscar Wilde wink, she defined elegance and class, especially after her wedding to Rainier.

"In 1952, she probably was the single most beautiful woman in the world," said Kelly biographer Jeffrey Robinson. "And then here comes Rainier, this handsome prince who owned a country. It's the stuff of fairy tales."

Though she starred in only 11 films, Kelly won instant critical approval and an Oscar. She captivated audiences with her work in some of the era's greatest pictures, including High Noon and Dial M for Murder .

Kelly's popularity during her life was unprecedented. First she made us fall in love with her screen presence. Then she became the embodiment of every bedtime story.

She captivates us today as an almost transcendent figure who represents the unattainable ideal of pure beauty and grace. She's never been the girl you could ask out.

Her mystery has only grown: She has been the subject of several books but has rarely been represented on film. (Her reputation is closely guarded by Monaco's royal family, who have resisted movies about Kelly.) The only notable exception is Cheryl Ladd's 1983 TV movie, Grace Kelly, which recounted her rise in Hollywood.

Monroe's mystique was always of a more explosive, earthy kind. She came from extreme poverty, a virtual orphan with a mad mother who made her way up the Hollywood ladder the hard way - often by way of sticky-fingered middle-age men's casting couches.

It took her many more years to reach worldwide fame, yet when she did, she yearned to be taken seriously as an artist.

And there was her tragic dependence on booze and pills and her untimely death.

"With Marilyn, the dysfunction and the sadness of her life and the way she had to battle her way up forms part of her image as a legend," said Taraborrelli. "She was a totally self-created and self-made woman."

Monroe's marriage to Arthur Miller proved she was not entirely unattainable. Even bookworms could get a date with her.

Though Monroe is forever young and beautiful, Kelly in the public eye had a family and grew considerably older before her own untimely death.

"She had grown into an entirely different kind of woman than she was in Hollywood," said Taraborrelli. "By the time we lost her, she had become a friend. So we felt her loss that way, as the loss of a friend."


Grace of Monaco

9 p.m. Monday on Lifetime

The Secret Life of Marilyn Monroe

8 p.m. Saturday and next Sunday on Lifetime