Fifty years ago this week, Valerie Solanas — a playwright and radical feminist — tried to kill Andy Warhol, shooting him in his Factory art studio on Union Square.

Margo Feiden believes she could have stopped the tragedy — if the police had just taken her seriously.

“It sounded ridiculous,” she admitted to The Post. “Me saying that Warhol is about to be shot. It’s like reporting a flying saucer in your backyard.”

Would-be murderer Solanas had moved to New York in 1962, after graduating from the University of Maryland with a psychology degree. Here, she started an organization called SCUM — the Society for Cutting Up Men, of which she was said to be the only member. She had also written a play, “Up Your Ass,” which Warhol found too profane to produce. He cast Solanas in the movie “I, A Man,” but she was said to hold a grudge against him for having lost the script to her play.

Apparently, that may have fueled her to try and kill him.

When she encountered Solanas, Feiden was 23 years old. Using the stage name Margo Eden, she was a theatrical wunderkind, having already produced a “Peter Pan” musical.

Now 73, Feiden has lived a charmed life: She’s raced camels in Egypt and earned her pilot’s license. Through her Margo Feiden Galleries, she has long represented the late caricaturist Al Hirschfeld. But that terrible 1968 day lives on with her.

“I think of it every day of my life,” said Feiden. “Even a can of Campbell’s soup reminds me of the day.”

The morning of June 3, 1968, Feiden was returning to her Crown Heights apartment with her young daughter, when she saw a stranger on her stoop. “She wore a heavy blue peacoat and a woolen hat” said Feiden. “I couldn’t tell if she was a man or a woman.”

Solanas introduced herself, saying she had something to discuss. The open-minded Feiden invited her up to the apartment she shared with her then husband, David, a social worker. Still bundled in her coat and hat, Solanas launched into an animated pitch for a play that she wanted Feiden to produce.

“She said that we needed to get rid of men,” recalled Feiden. “I wondered [about] women who want to have sex with men. She said she would keep a certain number of men in a bullpen, [with] numbers on their backs, and women could request them.”

Though Feiden could not argue with some of what Solanas said — men create wars and commit crimes — she made it clear that she would not be producing a play about eliminating any group of people.

Putting philosophical differences aside, Feiden liked Solanas. “I think we could have been friends. I found her intelligent and articulate,” she said.

Solanas went on for three and a half hours, her intensity not flagging as she revealed stories of being disrespected by men and raped by her father.

“Her pain was so tangible you could almost touch it,” Feiden recalled.

Then Solanas pulled something out of her bag. Aiming it at the ceiling, she asked, “Do you know what this is?”

“Yeah,” Feiden replied. “It’s a gun.’ ”

But Solanas wasn’t threatening her. “If you don’t agree that you will produce my play, I am going to shoot Andy Warhol,” Solanas said. “Then I will become famous, my play will become famous, and you will produce it.”

Feiden, however, felt no fear.

“If Valerie did something with the gun, that would be impolite,” she said. “And Valerie was polite.”

As Feiden finally guided her guest to the door, she couldn’t help but notice a sweaty stench of anxiousness emanating from Solanas — an odor that would linger in the apartment for days.

“She said, ‘I am going now to shoot him.’ I said she shouldn’t because it wouldn’t help her,” said Feiden. “I couldn’t say that it wouldn’t make her famous” — they both knew it would.

Feiden estimated that Solanas could reach the Factory within 30 minutes. She called the police precinct for Union Square.

“A woman was in my home and she is now on her way to shoot Andy Warhol,” Feiden told an officer. “She’s determined!”

But she was brushed off.

Feiden also phoned precincts near her home, the central station in Soho and even the office of Mayor John Lindsay — all to no avail. Feiden told one desk sergeant that Solanas had a gun. He replied, “How would you know what a real gun looks like?”

As she recalled, “It was the first time in my life that I felt I was being told something that would not be said to a man.”

She considered reaching out to her uncle Murray Feiden, a New York state Supreme Court judge. “I knew I could call him and that he could get the police to the Factory,” said Feiden. “But what would have happened if Valerie changed her mind? How would I have been able to face my family if I had called my uncle off the bench for nothing?”

Looking back, Feiden regrets her timidity. “Knowing the outcome, I wish I had done it,” she said. “I carried so much guilt and shame that I never told anybody about not calling my uncle, until now.”

‘It makes me sad that this is what she had to do to get famous’

Meanwhile, in Manhattan, Solanas entered the elevator at 33 Union Square and rode it to the sixth floor. She stepped into the Factory and asked for Warhol. He was out. So she planted herself in front of the building.

At around 4:30, Warhol returned and Solanas rode up with him on the elevator. He complimented her on the lipstick she uncharacteristically wore that day, then went into his office to have a phone chat with the actress Viva. Minutes later, Solanas confronted him and pulled her .32 caliber pistol from a paper bag. The first two shots missed their target. A third penetrated Warhol’s abdomen, ricocheting around his stomach, liver, spleen, esophagus and lungs.

Solanas also superficially wounded magazine editor Mario Amaya, and she tried to shoot Warhol’s right-hand man, Fred Hughes, but the gun jammed. She pulled a second gun out of the bag and aimed it at Hughes’ head but got distracted by the ding of the elevator. She turned, stepped in and left.

Warhol was rushed to Columbus Hospital on East 34th Street, where he underwent five hours of emergency surgery. Doctors gave him a 50-percent chance of survival.

Solanas made her way up to Times Square. Around 8 p.m., she handed her guns to an officer on 42nd Street, saying, “The police are looking for me.”

She was charged with attempted murder, felonious assault and possession of a deadly weapon. That summer, amid the post-shooting publicity, “SCUM Manifesto” was first published by Olympia Press.

Feiden still has the script Solanas handed her. “She gave it to me with great flourish,” Feiden said. “She was sure I would visit her in prison and produce the play.”

The police never interviewed Feiden about the shooting. For decades, she kept her story to herself: “I told my husband and eventually my daughter, but nobody else. I felt terrible.”

The incident weighed on her so much that she never read Solanas’ script — nor could she face anything to do with Warhol.

“I went to a dinner [party] once,” Feiden recalled. “My friend said, ‘Oh, do you know who you’re sitting next to? Fred Hughes!’ I turned white as a ghost and changed seats.”

Even though the murder attempt was not fatal, Feiden believes — and doctors concur — that it hastened Warhol’s 1987 death when he was 58 years old. For nearly two decades, the artist wore a girdle to keep his bowels in place, a consequence of an abdominal muscle split likely due to the shooting.

After a month of ill health, Warhol checked in to New York Hospital for gallbladder surgery; it was discovered he had gangrene, and he died less than 24 hours later.

As for Solanas, she was deemed mentally unstable, indicted on all charges and served three years at Matteawan State Hospital for the Criminally Insane. After her 1971 release, she again threatened Warhol, landing her back in a mental institute.

Solanas floated in and out of hospitals before a 1975 return to New York City. She spent the late ’70s on the streets of Phoenix and, in 1985, landed in San Francisco, where she was a sex worker. In April 1988, at the age of 52, she was found dead in her room, covered in maggots. The cause of death was said to be pneumonia.

Feiden has not seen the 1996 film “I Shot Andy Warhol,” starring actress Lili Taylor as Solanas. She watched the 2017 “American Horror Story: Cult” TV series, in which Lena Dunham played the shooter, for just a minute before switching it off.

Given the media acclaim that has come to Solanas, Feiden said, “It makes me sad that this is what she had to do to get famous.”

Despite trying so hard to avoid anything to do with the shooting or her weird afternoon with Solanas, Feiden actually did see her one more time.

“I was walking on Eighth Street [in the mid 1970s] and suddenly smelled something. I said, ‘Valerie is right here.’ [I saw her, but] I didn’t say ‘hello’ to her. I am ashamed of that. She died alone in a flophouse.”