Dyan Cannon said she sat around for two years writing music and lyrics and then she made up her mind:

"I want to be a rock 'n' roll star -- I'd like to do that more than anything else."

Amazingly, she got her chance: Tonight she appears in a two-part Disney movie called "Rock 'n' Roll Mom" (part one at 7 on ABC), playing out her fantasy.

"I was sitting here for two years, and when this movie came along, we just couldn't believe it."

It's not that Cannon has no background in music. "I used to play piano and conga drums and I opened for Sammy Davis Jr. at Caesars Palace about six years ago or so. I used to do Broadway musicals -- I love the stage and I love dancing." As Willie Nelson's wife in "Honeysuckle Rose" (1980), she made her film debut as a country music singer.

Since then, Cannon said, she has written "blues, ballads, a couple of rock 'n' roll songs, gospel, western," but hasn't recorded anything. For the Disney movie, "I actually did a couple of concerts, one at the Palace in Hollywood, the other in L.A."

In "Rock 'n' Roll Mom," Cannon plays Annie Hackett, a supermarket checkout clerk who switches gears at mid-life. With her best friends, Etta (Telma Hopkins), a beauty salon operator, and Connie (Nancy Lenehan), who works in a doughnut factory, she forms a singing group and becomes a rock 'n' roll phenomenon.

Aren't Annie's kids (Amy Lynne as Emma and Josh Blake as Nicky) embarrassed that good old mom has become an exhibitionist, leaping atop tables in a midriff-baring outfit to toss her mane about and sing their music? Aren't they annoyed that in order to pass as a singer now called Mystere, supposedly 27 and single, Annie pretends that her teen-agers belong to somebody else?

Cannon laughed. "That's why this movie is so cute, because that's all the things it's about: It isn't age -- it's attitude, it's about music and feeling. There's no age gap. The movie deals with all these things. The kids bring up the same questions.

"I have a lot of fun, and that's contagious. And I don't take myself too seriously ... It's a Cinderella story. It's about not settling for the broken set of dishes, about waiting for it all."

In some ways, Cannon has it all, too. Jennifer, her daughter by Cary Grant, is now 20, and not interested in show business, said her mother. Cannon has remarried ("Stan Fimberg -- he's in real estate"). She has appeared on Broadway, on television and in movies. She has been nominated for three Oscars, two for best supporting actress ("Bob and Carol and Ted and Alice" in 1969 and "Heaven Can Wait" in 1978). Her third was for writing, directing, editing, scoring and producing a 48-minute film called "Number One."

She has a New York Film Critics Award and a Golden Globe Award, and was once named best actress of the year by the National Association of Theater Owners, and Female Star of the Year by the Hollywood Women's Press Corporation.

"I'm finding now that is really is my turn, time for me to explore new avenues of thought," said Cannon. "It's how we feel about things and feel about ourselves that matters. What other people think isn't as important to me anymore."

A former model, Cannon made her television debut in 1959 on a CBS daytime serial called "For Better or Worse" and in prime time on NBC's "Bat Masterson." She continued on television, appearing most recently in CBS' production of Sidney Sheldon's "Master of the Game" in 1984 and in "Jenny's War," a four-hour film in which she played an American woman seeking information about her son, a British flier shot down over Germany.

She appeared on Broadway in "The Fun Couple," with Jane Fonda, Ben Piazza and Bradford Dillman, and starred for 18 months in "How to Succeed in Business Without Really Trying."

In 1960, Cannon made her first movie, "The Rise and Fall of Legs Diamond," and went on to appear in more than a dozen films including, in 1982, "Author! Author" and "Deathtrap," in which she played the hysterical wife of Michael Caine. Recently, after turning down roles that she said "weren't interesting enough," she agreed to appear in "Caddyshack II" with Chevy Chase and Dan Aykroyd.

So, after three years or so, Dyan Cannon is back at work. She's still glamorous, and a look at "Rock 'n' Roll Mom" shows that she is also very trim -- as befits a middle-aged mom playing a 27-year-old rock star.

Cannon turned 50 in January.

Her secret -- besides a youthful attitude -- is something she calls "food combining. I don't mix foods that don't work for me: If I eat potatoes, I don't eat meat. I don't mix carbohydrates and protein. I was a vegeterian, but I eat fish now, a lot of nuts and seeds. I eat well -- three meals a day. And I don't weigh myself. Since I've stopped weighing myself, I've lost a lot of weight."