In "Lorenzo's Oil," Susan Sarandon plays the real-life role of Michaela Odone, who, with her husband Augusto, fights to find a cure for a rare disease that is destroying their 5-year-old son.

Sarandon is tall and imposing. Mrs. Odone is small and almost birdlike. But they have at least two things in common: They are both mothers, and both have been described as ferocious."Susan has that ferocious, primitive mothering instinct," says "Lorenzo's Oil" director George Miller, who first worked with the actress in the troubled production of "The Witches of Eastwick." "And it's natural that she should wind up playing Michaela. Of all the people involved in the project, she was the first one to be aware of the real story."

Sarandon first listened to tapes made by Mrs. Odone four years ago. That was four years after the Odones had discovered that their son Lorenzo suffered from adrenoleukodystrophy (ALD), a disease for which there exists no known cure and which robs male children of hearing, speech, movement and eventually their very lives. The Odones set out to find their own cure for the illness.

"At that time, I was with the father of my daughter, and he wanted to make a film out of the Odone's story," says the actress, referring to the Italian director Franco Amurri.

"He brought Michaela's tapes home, and I listened to them again and again. They were made at the height of her fury, when she felt such dismissal by the medical community and had such intense emotions inside her. She spoke with such passion, drawing parallels between herself and Augusto and the AIDS activists. What drew me into the story so intently was the AIDS parallel."

Ironically, during the filming of "Lorenzo's Oil," Sarandon discovered she was pregnant.

"I was thrilled to be pregnant, but at times the circumstances were disturbing," she says. "We were working with disabled children, many of whom had been damaged by incompetent birthing. They were so sweet, so loving. They would just pierce your heart.

"Making the film was very draining and cathartic but not depressing. I have too many children to indulge in depression. Tim (Robbins) was directing, writing and starring in `Bob Roberts' at the time I was making `Lorenzo's Oil.' I had to keep myself together for my children."

Born Susan Tomalin, she was briefly married to Chris Sarandon, best known for his roles as Al Pacino's lover in "Dog Day Afternoon" and as an enthusiastic torturer in "The Princess Bride." She has a 6-year-old daughter, Eva, by Amurri. She and her current companion, Robbins, whom she met on the set of "Bull Durham," have two sons: 3-year-old Jack Henry Otis Robbins and Miles Guthrie Tomalin Robbins, who was born last May.

Sarandon is known as a gifted, outspoken actress who avoids the Hollywood scene in favor of New York. A week before she was to play the "head witch" in "The Witches of Eastwick," with Jack Nicholson, Cher and Michelle Pfeiffer, producers Jon Peters and Peter Guber, possibly at Cher's urging, decided that she and Cher should switch roles. Sarandon stayed in the film but the event rankled her.

"Of course, there was some bad blood at the time, but they were all with Guber, Peters and Cher and were fairly easily put aside," says Miller, director of both "Witches" and "Lorenzo."

Sarandon isn't so sure.

"I went through a terrible time with George when they took my part away and gave it to Cher," she says. "It couldn't all have been Peters and Guber. George was the director. He had some say-so, don't you think?"

In any event, the director and actress found themselves sitting next to each other on a plane ride. He told Sarandon that Pfeiffer, ironically her other co-star in "Witches," had been cast in "Lorenzo's Oil" but had dropped out.

"Michelle got cold feet, and also, about that time, she was cast in `Batman Returns,' " Miller says. "Michelle is like Michaela at the core but not externally. I was interested in how she would stretch herself."

As they discussed the Odones' story on the airplane, both Sarandon and Miller realized each other's commitment to the project. Sarandon was cast.

"George felt great passion for the story, so I was willing to set aside what happened on `Witches,' " she says. But her hesitation next had to do with Nick Nolte, who plays Augusto and had been in constant rehearsal with Pfeiffer.

"The movie calls for a very specific husband-wife relationship," she says. "In the film, Nick and I never touch, never have physical intimacy, hardly ever even look at each other. But it's necessary that the audience feels our emotional bond. Augusto and Michaela just do whatever is necessary. They get up and take care of the problems of the day. I'm very proud that Nick and I seem like we're really married and have been for years."

Once production started, problems possibly occurred in another form. According to an article in Premiere magazine, Zack O'Malley Greenburgh, the most prominent of the six actors who play Lorenzo, was a source of trouble on the set. The article suggests the young actor was prodded by his parents to behave in a difficult manner.

"They were shameless," says Miller of Zack's parents. "They wanted to sell a screenplay to us. They wanted credit as coaches. They needed us for self-esteem because they were going through a divorce. They used the film shame-lessly."

Sarandon is marginally more diplomatic but still gets her point across. "If you think I'm going to bad-mouth a 6-year-old, you're out of your mind," she says. "But it's horrible to work with someone who doesn't want to be there. It's just awful. But I'm not going to get into it. Not at all. Were his parents simply trying to protect him? Well, `protect' is not the word I would use."

The story of the Odones' search for a cure for ALD already had been made into an Italian television film. The telemovie had not met with the Odones' approval.

"There was some apprehension on Michaela's part about the story becoming a Hollywood film," says Sarandon. "She's ferocious and uncompromising. She challenges everything where her child is concerned. She's fierce. But anyone who has kids knows that you just resign yourself to the fact that, during their first year, you are not going to get any sleep. Michaela's entire life is like that."

A political activist, Sarandon always has been outspoken in her skepticism of authority figures. "I was delighted when `Thelma & Louise' stirred up trouble," she says, laughing.

The experience of filming "Lorenzo's Oil" did nothing to soften her views.

"It's quite clear that research in this country is not motivated by the patient's best interests," she says. "Scientists are motivated by grants rather than by the time frames of patients' lives. Most doctors are pretty patronizing in terms of people having choices over their bodies. The AMA (American Medical Association) is greedy and corrupt. But we shouldn't blame them as much as people who simply hand their lives over to authority figures, and that includes lawyers and government officials as well as scientists and doctors. Michaela and Augusto are ordinary people who became extraordinary because of their refusal to bow down."