For three days Margot Kidder wandered the streets of this city, dirty, penniless, delusional and quite alone. The actress best known as Superman's girlfriend -- a household name, a recognizable face -- went undetected as she walked and rode from Los Angeles International Airport to the tree-shaded streets of suburban Glendale, where police found her last week cowering in a back yard with her hair hacked short and her front teeth gone.

Those confused 72 hours were the most tragic -- and the most public -- of a career that went from obscurity to stardom to addiction, bankruptcy and, finally, mental breakdown. Kidder is being treated in an undisclosed private psychiatric clinic here, with her family at her side. She is no longer alone, except in the glare of unwanted fame.

Faster than you can say "speeding bullet," the doors of Hollywood have swung shut. Variety and the Hollywood Reporter dispensed with the affair with wire service reports. No one in the publicity department at Warner Bros., the studio that produced the Superman movies, could seem to call up any memories of the actress who starred in all four productions, nor muster any thoughts on her current predicament. Dozens of people in Hollywood know Kidder well; a dozen ignored interview requests. Even their agents declined to pick up the phone, and Kidder's own manager, John Blake, hung up with a terse, "I'm protecting her confidentiality. Sorry. No. Bye."

It would be tempting to regard Kidder's story as a morality tale in the age of hollow celebrity and media hype. It would be easy to see her as the victim of a heartless industry that builds its idols only to break them down with neglect and derision. Hollywood Babylon.

That no doubt is part of the story. But those who know her say that Kidder played a central role in this drama of public self-destruction.

When she finally speaks, she may say the same herself. Three Days

Police and witnesses have given a sketchy account of what happened to Kidder in the 72 hours she was missing. She showed up at the Los Angeles airport on Saturday night, April 20, for a flight to Phoenix, on her way to teach an acting class at Eastern Arizona College. Except that her flight was not until Sunday.

She wandered around the airport for several hours, talking to security guards and some travelers. About 3 a.m. she approached Ted Hall, a television reporter from Knoxville, Tenn., and his cameraman as they debarked a flight from Atlanta.

"Out of the corner of my eye I saw a woman approach us from the metal detector area," Hall says. "She said, Are you folks with the media?' We said yes. She said, I'm Margot Kidder. Do you mind if I hang out with you guys?' " According to Hall, she was wearing a black pantsuit and a white shirt smeared with dust and makeup, as if she had used it to wipe her face, and carried no purse or luggage.

Appearing frightened, Kidder told the journalists that she was being stalked by several men hired by her ex-husband, a writer, to kill her. (Kidder was married in the 1970s to fiction writer Thomas McGuane.) "He makes O.J. Simpson look like Alan Alda," she said. At first they believed the story, but when Kidder pointed out a man at the luggage claim area and said he was following her, Hall knew something was wrong. The man had been on their flight from Atlanta.

Kidder's behavior, Hall says, was strange. She did not want to call the police, and she asked Hall for a disguise, or at least to switch jackets with her, because her jacket "was bugged." Communicating sometimes by writing notes, Kidder asked for money -- taking a $20 bill and returning all but a dollar after making change -- and asked the two to call her a taxi. She left the airport about 4:30 a.m.

The taxi driver, it appears, soon ejected Kidder from the cab because she was broke. For much of the next two days, police say, she wandered for miles on foot and hid from phantom stalkers. She approached three people on the street in Atwater, north of the airport, asking for a cigarette. By that time she had lost her dental plate and was wearing a rumpled red sweat shirt and blue pants that police say she got in a swap with a transient. Believing she was homeless, the three gave her a ride to Glendale and offered to help her find a place to sleep at a homeless shelter. The shelters were full, so they paid $33 for a room for her at the Bell Motor Motel at about 11 p.m. Monday.

"She looked awful," says motel manager James Rauch. "She looked like a homeless person." Kidder, who signed in as E.S. Brown, stayed there overnight, barricading the door with a shelf from the closet. The next morning she appeared at the front desk wrapped in a bedsheet, asking Rauch for change to dry her clothes, which she said had fallen into the shower. She also borrowed a pair of scissors and reappeared with her shoulder-length hair haphazardly chopped short.

Police say Kidder spent most of Tuesday walking the streets of Glendale, until about 6 p.m., when police, alerted by a homeowner, found her behind a bush in a back yard on Ross Street.

They describe her as disoriented. "She had told us she had been staying there for several nights, but that in fact was not true," says Sgt. Rick Young, adding that the actress showed "paranoia rather than fear. If you're a cop, you recognize fear, you live with fear. The officers on the scene said it was a classic case of paranoia."

Police, who found no indication of drug use, took her to the psychiatric ward of the county's Olive View-UCLA Medical Center in Sylmar; last Wednesday she was transferred to a private clinic. She has since twice refused to talk to police.

When Kidder failed to appear at the Phoenix airport on Sunday night, college officials in Arizona contacted Blake, her manager. Bewildered on hearing the first reports of her reappearance, he told the local media, "I don't know what's going on. . . . Margot didn't appear to be wrestling with anything. She had been working steadily. Her spirits were high." Slow Fade

Which is, actually, a slight exaggeration. In fact, Kidder, 47, had been struggling to make a comeback after a merciless run of personal, professional and financial misfortunes.

Born in Yellowknife in Canada's Northwest Territories, where her father was a mining engineer, Kidder first became interested in acting when her family moved to Toronto. Her career began in the late 1960s with small roles in forgettable movies such as "Mr. Mike's Mondo Video." She tended toward brassy, hard-headed characters that suited her attractive but unglamorous, angular features.

Kidder's fame peaked in the late 1970s and '80s with the "Superman" series, in which she played Lois Lane to Christopher Reeve's Man of Steel; the first two were blockbusters. She had roles in other, moderate hits, including "The Great Waldo Pepper" and "The Amityville Horror." At the height of her career she was the best-known, best-paid Canadian performer in the United States.

By the late 1980s Kidder's star had begun to fade, but her luck turned decidedly sour when she attempted to make a film of Margaret Atwood's novel "Lady Oracle." She spent a fortune developing the idea into a screenplay, but ultimately could not find a backer.

Then real disaster struck. In 1990, while in Vancouver filming a cable series based on the Nancy Drew mysteries, Kidder injured her spinal cord in what initially appeared to be a minor car accident. Resisting doctors' recommendations for back surgery because it involved the risk of paralysis, the actress suffered persistent pain, and told People magazine in 1992 that the painkillers she was taking left her mind "muddied." Surgery eventually corrected the ailment, but Kidder's insurance company refused to pay the bills, and the Canadian production company's insurers rejected her claim, saying she was not injured on the set.

With six figures worth of medical bills, Kidder went bankrupt, losing her home in rustic Sneden's Landing, N.Y., and at one point selling her jewelry up and down the diamond district in Manhattan to raise cash. By 1992 she was living in a one-bedroom apartment near Hollywood and driving a 1986 Chevy Blazer; her father had died, and her teenage daughter had developed an eating disorder. "There were days I just desperately wanted to die," she told People.

In the midst of her career struggles, Kidder was a liberal political activist, speaking at rallies during Jesse Jackson's 1988 presidential campaign, denouncing capital punishment and fighting for abortion rights. She also opposed the 1991 Persian Gulf War, writing an article in the Nation to explain her position.

In recent years, Kidder had seemed determined to fight the tide of adversity that threatened to drown her. She began working on an autobiography, tentatively titled "Calamities," and took work where she could get it, doing voice-overs and appearing in guest spots on "Murder, She Wrote" and "Tales From the Crypt," and in a CD-ROM thriller called "Under the Killing Moon." She co-starred with Stacy Keach onstage in Baltimore last year in "Stieglitz Loves O'Keeffe: Flowers and Photos," and moved to Livingston, Mont., to be closer to her daughter, Maggie, who was married last summer to writer-journalist Walter Kirn.

Kidder's last project before last week's ramble was "Never Met Picasso," a small independent film, budgeted at about $100,000, in which she played an avant-garde theater actress and the mother of an artist (Alexis Arquette) struggling with a creative block. The film, which does not yet have a distributor, was shot in Boston last October and November.

"Picasso" producer Patrick Cunningham says Kidder showed no signs of mental fragility at the time. "She was wonderful," he says. "She always uplifted everyone's spirits by joking, cheering us up. She was always on time, always professional."

But a source close to Kidder's family says her behavior had become erratic. "There have been past incidents in which she was delusional, paranoid," says the source, who spoke on condition of anonymity. "It was total lunacy -- saying that other people were out to get her, were after her money. Just generally unstable behavior." It Was the '70s'

None of Kidder's ex-husbands -- there are three -- would seem to be out to get her, least of all Thomas McGuane, who was married to the actress for less than a year and has been married to his second wife, Laurie, for the past 18. McGuane, who lives on a ranch near Big Timber, Mont., says he has barely seen Kidder in the past 20 years.

"We did not have a successful marriage," says McGuane, the author of "The Missouri Breaks" and other novels, reached at a horse competition in Utah. "We had a brief marriage, and I left it with a tremendous sense of relief." The relationship was doomed early on, according to the writer. "It was Superman' time, it was the '70s," he says. "It was a hit-and-run sort of era."

Of the relationship, Kidder once said, "I spent four years being drunk a lot of the time."

But McGuane and Kidder did see each other last year, at the wedding of their daughter, Maggie, now 20, who was mostly raised by her mother. McGuane says Kidder's accusations of stalking -- even coming from someone under psychiatric care -- are hurtful.

"I don't even know how to react to it. I've barely seen her in over 20 years," he says. "It's a shame she's had the trouble that she has. I'm sorry she continues to have the feelings toward me and my family that she's expressed. I'm afraid I can't tell you why {she has them}." He added, "My biggest concern is that this is extremely painful for Maggie."

Kidder's daughter appears to be the one constant in her life over decades of shifting loves and friendships. The actress met her second husband, actor John Heard, in 1979, when they both got parts in the Paul Mazursky film "Willie & Phil" (Heard later dropped out); their relationship ended a year and a half later. But even that union was long when compared with Kidder's 1983 marriage to French director Philippe de Broca. They met on the shoot of a cheesy Civil War miniseries; the marriage was over by the movie's premiere.

The actress had many other love interests, from director Brian De Palma to former Canadian premier Pierre Trudeau. The wheelchair-bound Christopher Reeve, who issued a statement of support last week, has been a longtime friend, and in recent years comedian Richard Pryor, who suffers from multiple sclerosis and knows the sting of Hollywood's rejection, has given moral and sometimes financial support.

But for most of the past six years, at least, Kidder has been alone. Hollywood, well known for adoring its success stories, has an equal and opposite reaction toward its failures. Cunningham, the independent film producer, seems more than a little naive -- or simply crass -- in his insistence that Kidder will be on her feet to promote "Picasso" in no time.

"I hope without a doubt to see her before that point. It's already planned," he says. "With a little rest -- I can't even imagine a long rest -- she could be another lead in a movie."

But at least one police expert sees things differently. "When we get involved, everything has fallen apart -- that means there is no family, no friends, no mental health getting involved," said Detective Walter Decuir of the LAPD Mental Evaluation Unit, which intervenes in these sorts of cases. "We assume responsibility for mental health by default. And we are the least equipped in the chain to handle it." Falling

Even when they're not that big, they fall pretty hard in Hollywood.

The difference with Kidder is that she did the unthinkable: She abandoned all pretense to stardom. She begged to be noticed in her delusions. She caved in the most painfully public of ways.

If Kidder's misfortunes seem to be equal parts bad luck and bad judgment, Thomas McGuane, for one, believes that it's wrong to blame Hollywood.

"Hollywood doesn't do this to every person," he says. "Hollywood is about as capable of delivering personal evil as the Bank of America -- it's a big, corporate, soulless industry. To invest it with the power of evil is pretty fanciful."

The best judge of that appraisal, of course, has yet to speak. Until she tells her story, the only words we have are the notes she gave to Ted Hall that night in the airport:

"Just pretend I'm with you, if you could, until I get a taxi." And then, "Take my jacket with you a few miles and then throw it away." Finally, frantic, before getting into the taxi and driving away: "I am DEAD."

And somewhere in Babylon, someone is surely negotiating the deal for the made-for-TV movie, Hollywood's final indignity on a celebrity corpse. CAPTION: Margot Kidder at Wolf Trap in 1986, right; and, from top, with Christopher Reeve in "Superman" (1978); in "The Amityville Horror" (1979); with Richard Pryor in "Some Kind of Hero" (1982). CAPTION: Margot Kidder in a 1979 photo with an unidentified escort.