With her icy beauty, withering stare, and the British accent she wields like a poison dart, Stephanie Beacham might be the one to show Joan Collins the real meaning of she-deviltry. Dynasty co-creator Esther Shapiro certainly thought so when she signed the auburn-haired, hazel-eyed British actress to play Sable Scott Colby, Charlton Heston's wily wife and mother of his three heirs, in The Colbys. Okay, Shapiro didn't scream, "Get me Beacham!" in the first flush of casting. Faye Dunaway, Angie Dickinson, Elizabeth Ashley and Diana Rigg all turned down the role before Beacham even heard about it. But since the debut of The Colbys in November, Stephanie has proved to be the show's real fire. When Heston's sister, played by Barbara Stanwyck, gets in her way, Sable retaliates by trying to have the family matriarch declared incompetent and loosening the girth on Stanwyck's horse hoping that the old girl might take a fatal tumble. So far Beacham and Collins, who plays Sable's cousin Alexis, haven't had a face-off yet. But Beacham allows having a go at it might be "jolly good fun."

Beacham, 39 this month, opens the door of her trailer on The Colbys set festooned in diamonds and emeralds (they turn out to be $400 worth in paste). She flashes a no-nonsense look that delivers what it promises. "People think I'm snotty because I ignore them," she says. "I just don't hear them." Beacham is completely deaf in her right ear and has only 70% hearing in her left. She compensates by playing as many scenes as possible on the right-hand side of another actor. Early on in the series, when Beacham was most nervous, co-star Linda Evans showed understanding. Even when the scene was set up differently, "Linda just quietly manipulated me around to her right side. She's a doll."

Beacham explains that her main reason for doing The Colbys is her pay, an estimated $20,000 per episode. "Look," she says framing her face with her hands, "5 more years for this face, friend, maybe 3." Her appearance, she says, never interested her. "Then I realized that if I wanted to do film work, I'd better do it now."

She almost missed her shot at The Colbys. Exhausted from completing her role as ruthless business woman on the 1985 hit British series Connie, she was on vacation when asked to return to London to screen-test for the part. She was ready to pass when a neighbor she's entrusted with the care of her town house phoned to confess that she'd locked the keys inside. Beacham had to return or face a cemetery of dead plants and fish. Tested on a Friday ("I said whatever rubbish I could remember and camped it up"), Beacham was flying to L.A. a week later, and by the next day she was sitting in wardrobe. "We loved her patrician quality," says Shapiro. "Despite Sable's seamy side, you can understand why a major tycoon would stay married to her."

Beacham's training at the Royal Academy of Dramatic Art helped nurture that classy demeanor. But she had to get through some "corking bad horror films" before winning prestigious roles, such as in The Nightcomers with Marlon Brando in 1971. Beacham is proud of the success she's since achieved (The Homecoming), but they paid scanty sums. Getting famous in America represents the ultimate financial jackpot. She reports that her parents - her father is a retired real estate administrator and her mother, a housewife- are appalled that she's "chasing the dollar and that everybody is thinking of me as a bitch."

She's doing it anyway, for two reasons: daughters Phoebe, 11, and Chloe, 8, whom she had already placed in a boarding school 20 minutes from her parents' home in rural Somerset. "They are my love affair," says Beacham, who phones them once a week and sends a letter every Tuesday. Though The Colbys has upped it's initially sluggish ratings, there is no official guarantee as yet for a second season. Until there is, Beacham has no intention of uprooting her family. "It's funny- I wouldn't have been interested in doing commercial work like this if it weren't for them, and now the work is taking me away from them."

That kind of domesticity helped end Beacham's marriage to the girls' father, actor John (Mercutio in Zeffirelli's Romeo and Juliet) McEnery, 42. "He was a rotten person to marry but a lovely friend," she says. Beacham left what she calls "her cozy red-velvet-curtained" childhood (she has one brother and two sisters) to live as a happy hippie doing theater before wedding McEnery in 1973. But, she says, with two children, "one of us had to get grown up, and it was Mum." Although separated for 8 years, they have not divorced and have no plans to so do. "He is the father of my children," she says. "We are irrevocably linked. Not being divorced acknowledges what we have produced."

While her heart remains in England with her daughters, she lived in 2 rented homes, one in Hollywood, one in Malibu next to Tracy Scoggins (her TV daughter Monica Colby). Beacham's idea of fun is housework. "It's pathetic, isn't it?" says a laughing Stephanie.

Beacham admits to bouts of mild depression, "You want to see me cry?" she challenges. "Let's talk more about my children." Many nights she finds herself standing in front of the fridge what a script in one hand and foraging for something to nosh with the other. There are magical moments, however. "One day I was sitting on the set," she says, "and I suddenly thought, 'My God, this is Hollywood!'" Plans for tonight are less the glamorous. It's home and into jeans, sneakers and old sweatshirt. If there is time after running through her next day's lines, Hollywood's hottest new bitch might dash off a letter to her children.