She needed a few inches of topside padding plus a breakfast diet of doughnuts and bagels to ripen into the title role of ABC's Marilyn: The Untold Story. And that may be just the least reason why Catherine Hicks, 28, seemed miscast snuggling between the satin sheets as Monroe, the tragic sex goddess. Hicks, after all, is a natural brunette, a beloved daughter long cossetted by her proper upper-middle-class family and an alumna of Notre Dame's sister school, St. Mary's College. But there was an empathy. "It sounds corny, but Marilyn was like a sister I didn't have," says Hicks. "The acting was like exhaling, like I released something."

Catherine released even more than will be seen in the scheduled September 28 TV special: She shot a completely bare skinny-dip scene for the overseas movie-house version of the $3.5 million production. As for the upholstering to her own lithe 34-22-34 figure, Hicks observes, "I don't know if I'd like to be voluptuous all the time, but I did feel a certain extra femininity that was fun, and it was a joy to have my dress billowing in the breeze. But now I've put that character to bed," she insists. "I've gotten the 'lonely blonde' out of my system."

But perhaps not out of her life. Since breaking up in 1979 with her actor boyfriend of three years, Catherine complains that many of the Hollywood men she met "just wanted to take me to Palm Springs for the weekend." Though she hates "to blame the breakup on the old career thing," Hicks notes, "It's hard to keep a romance together until you reach a plateau where you can rest easy—and I'm certainly not there yet." Even the recent 10th reunion of her high school class made her feel a little behind. "Everyone was all married, settled and happy," says Hicks. "They looked at me like, 'Poor Cathy.' It was obvious that I was still out on the ocean charting my course."

There seems small doubt that Cathy will find the safe harbor that eluded Monroe. The stable family behind her will try to insure that. Monroe never knew her father as a child and was abandoned to a foster home at the age of 12 days, after her mother's mental breakdown. The Manhattan-born Hicks, by contrast, grew up in the snitzy desert suburb of Scottsdale, Ariz., the daughter of an importer and a housewife, "I understood what it was like to be an only child, though," Catherine points out. "There weren't a lot of kids to play with, and it's kind of tough to climb a cactus, so the imaginary world was my backyard."

After distinguishing herself as the fastest typist (85 wpm) at Scottsdale High—"Typing's still a fallback," she jokes uneasily—Hicks studied drama at St. Mary's. Following her graduation in 1973, she won an acting fellowship to Cornell. There, ironically, she landed lead roles in Bus Stop (the part Marilyn made famous) and in After the Fall, playwright Arthur Miller's expiation of his turbulent 1956-1961 marriage to Monroe. After two years in New York as Dr. Faith Coleridge in the ABC soap Ryan's Hope and in Broadway's Tribute with Jack Lemmon, Hicks moved to L.A. in 1979.

"I came here with the 'New York Princess attitude,' " she recalls ruefully. "I assumed they would meet me at the plane with roles because I had just come from Broadway. But if you come with that attitude, this town kicks you in the stomach." Under the same pressures, Monroe propped up her ego with pills and therapists, but Hicks declares that she doesn't touch the former, and has "never had a shrink or felt the need for one. We've all been shrinked enough."

Instead, she just relaxed. "Once you open your arms and welcome L.A., it welcomes you back," Hicks beams. "Literally, one day, I don't know why, I woke up and felt loved—well, accepted at least." That, sadly, may be the one emotion Catherine won't need this week to capture the haunting spirit of Marilyn.