Joan Collins, executive producer and star of "Sins," was sitting in the dressing room on the set of "Dynasty," where she is only a star.

She was having a harried lunch break, munching on a sandwich while trying to complete a telephone call. From the door came two frantic calls from a makeup person.

"That," she said, "is the difference between being a producer and being an actor," the difference between being a mover and shaker and the moved and the shaken.

To her, being able to be a mover and shaker is one of the niftiest things about her three-night miniseries, "Sins." "This is something I feel I must do," she said of her role as executive producer, a job she's undertaken only once before but is obviously looking forward to assuming again. When you're an actor, you do what you're asked when you're asked. When you're a producer, you do the asking and you can even put yourself in your own film.

Exhibit A in her case for becoming an established producer as well as a star is the seven-hour "Sins," beginning at 8 tonight on CBS and running through Tuesday.

Collins plays Helene Junot, head of an international fashion magazine publishing empire headquartered in Paris. The series includes all the pot-boiling elements we've come to associate with the parts Collins plays -- romance, high ambition, glamor and revenge.

Now add responsibility.

"I had a great deal to say about casting," said Collins, whose co-executive producer is her husband, Peter Holm. "I had to fight over some of the parts" to gather a group not overly exposed in miniseries.

Featured players include Jean-Pierre Aumont, Marisa Berenson, Joseph Bologna, Capucine, Arielle Dombasle, James Farentino, Lauren Hutton and Gene Kelly.

And she is enthusiastic about her choice of Neil Dickson, previously seen in the lightly-viewed "A.D.," to play a decadent nobleman obsessed with Collins.

"The role is a challenge to me," said Dickson, who's used to playing good guys. He was impressed with the cast Collins helped assemble. "I looked at the list," he said, "and mine was the only name I didn't recognize."

"And," said Collins, "I was involved in the look of the show. If you're going to do a show that spans 43 years . . . " she stopped to wave off the makeup person. "Where were we? Oh, yes. There are too many miniseries in which they put a sign up that says 1959 and they're in modern clothes, cars and so on. I had to fight to the finish. One thing I wanted to be was absolutely authentic."

There are a number of impressive production parts assembled for the show. The score was done by Oscar-winner Francis Lai ("Love Story"), with added music from Michel Legrand. Carly Simon sings the title song, which she helped write. Michel Fresnay, who dressed the characters in "Mistral's Daughter," was the overall costume designer. Collins wears more than 35 outfits stitched up by Valentino.

It promises to be a lush-looking series, sounding many of the melodramatic themes Collins has come to be associated with. Airing amid drooping "Dynasty" ratings, "Sins" may test her staying power as a star as well as her abilities as a producer. Just how well does this show have to succeed?

"I'd like it to finish in the top 15 for the week," she said. "I'd like it to win the night, all three nights. And I'd like for it to get a 25 share, but people are hoping for better."

"Sins," which Collins said cost $13 million to make, is pitted against "Peter the Great," a $26.5-million man, for three nights.

"It's dog-eat-dog," said Collins of the duel of the miniseries. "I'm flattered that NBC scheduled us the first Sunday in a sweeps month. I'm not surprised that CBS put their big guns up against us."

She downplayed the idea that "Sins" might be seen as an extension of the "Dynasty" style. "This is more realistic than 'Dynasty,' a more realistic story." She acknowledged the ratings sag in her regular series and blamed the show's writers.

"I said at the beginning of the season," she said, biting her sandwich but not her tongue, "that the scripts were awful. The producers said, Look at the ratings. Yes, I said, but those were for past scripts. Look at this one."

A real problem, she said, was that a lot of the starch had been taken out of Alexis. It's now being put back in, she promised.

"She was losing her grit, juice and bite," she said. "I became a woman the public likes because of Alexis' aggressiveness, grit and bitchiness."

And the aggressiveness shows in Collins' own drive to produce, to call the shots.

"It's the only way an actor or actress can control what they do" and when they do it. "Actor are like books," she said, "waiting for a producer to check them out and then put them back on the shelf."