The barn-raising scene in Peter Weir’s masterpiece, “Witness,” is one of the most perfect pieces of pure cinema the movies have ever produced.

Beautifully conceived, shot (by future Oscar winner John Seale), edited (by Oscar winner Thom Noble) and scored (by three-time Oscar winner Maurice Jarre), it informs, moves and underscores the dilemma and love triangle dynamic at the heart of this classic almost without words.

Looks are exchanged between the on-the-lam cop (Harrison Ford) “passing” for Amish, the wide-eyed Amish widow (Kelly McGillis) and her more suitable suitor (dancer/actor Alexander Godunov) from her rural Pennsylvania community. Disapproving scowls are glimpsed from her stern and elderly father-in-law (Jan Rubles). And screen newcomer Viggo Mortenson gapes and grins and takes it all in, a balletic trio acted-out in stares of longing, staredowns and smiles between saw-strokes, hammer blows and twists of the hand drill.

It’s so perfect that this single scene can’t fail to produce tears, not just for the romance-that-should-not-be or should-be, but for “community,” the earnest generosity of people pulling together for a common goal.

When we talk of movies in “They don’t make’em like that anymore” terms, we’re not just speaking of epic productions of the past and their “cast of thousands.” “Witness” captures a great filmmaker in his prime and a star coming into his own depicting an Amish community that has changed much in the intervening decades and an America that has changed as well.

But we can go back and watch that barn-raising scene and at least hope the community connections, values, the urge to do the right thing and find fulfillment, happiness and justice can stage a comeback.

A couple of veteran TV writers specializing in Westerns such as “Gunsmoke” and the series version of “How the West was Won,” Earl K. Wallace and William Kelley, conjured up this Oscar-winning story of an Amish family and a police detective who run afoul of murderously corrupt cops and must lay low in Amish country.

A St. Paul-quoting “Come out from among them and be separate” culture with no phones, no cars and little connection to the world of “The English,” as they call America in the film, it was a stroke of genius realizing that these people would make a great hiding place for a child witness (Lukas Haas, amazing) to a murder and a cop wounded as he tries to protect that Amish boy and his mother (McGillis, in her breakout film role).

Weir, fresh off of “The Year of Living Dangerously,” keeps the romance on low-to-high simmer with scene after scene of McGillis drinking in this tough, heroic and manly cop like a widow dying of thirst. And he handles the many set-pieces — action and otherwise — with a surehanded skill that should be taught in film school thriller classes.

The child is unlucky witness to a murder in the Philly train station bathroom, and this sheltered boy’s gaping shock and plucky, think-on-his-feet reaction becomes one of the signature moments of the movie. Likewise, when Haas’s Samuel wanders the police station where John Book (Ford) and his partner (Brent Jennings) show him police line-ups and mug-books of photos, only to have the child spy a photo commemorating the murderous cop (Danny Glover made great villains back then) is another piece of acted, shot and edited perfection.

The boy stares at Book across the room and silently points at the photo, with Ford slowly taking the kid’s hand and balling up that accusing finger because they don’t know if they can trust anybody in that precinct.

“Witness” covers familiar police procedural ground in violent bursts — Book and partner rousting a bar and mashing a suspect’s face against a police car window — and mesmerizing pauses, just like that moment of recognition.

The betrayal and violence that send Book and Rachel and young son Samuel on the run puts them back on the farm where she lives with her father-in-law ends with a slow-motion crash between a bleeding-out-Book in his sister’s VW Squareback and a huge birdhouse on a pole.

What follows, as Book is nursed to recovery and takes stock in what options he has, is a gentle culture clash comedy with serious undertones. He learns to milk a cow. He revives his latent carpentry skills. And he tries not to fall in love with the young widowed mother who fears the influence of a “man with guns” given to “whacking” people over her son, but who is plainly smitten by the decent person he seems to be — profane and tempermental or not.

The tall, lean and charismatic Russian defector/dancer Godunov almost steals the picture as the stoic but good-humored neighbor who comforts Rachel with an eye towards courtship and another eye on the “Yankee” she has staying with her under her roof.

“You look plain, Book. Very plain.”

But barn-building or not, Book’s headed for a reckoning with the world he left behind. And when it comes, “old ways” and community will face off with violence and the pitiless men with guns and badges who wield it.

Weir, already proven as a filmmaker at home with drama, action with lighter moments and “communities” in his films, would trot out that mastery here and later with “Green Card,” “Master and Commander: The Far Side of the World,” “The Truman Show,” “The Way Back” and “Dead Poet’s Society.”

He makes “Witness” a movie of grace notes, grim violence and touches of humor. Book is wary and wry about the “quaint” Amish, and Weir lets us see bits of bawdiness in this tightknit, Bible-based enclave.

We see the wind breezing through the barley, hear Harrison Ford sing along with Sam Cooke on “What a Wonderful World” and catch Godunov’s Daniel showing off for Rachel and Samuel, racing his wagon beside the train they’re leaving on, striking a heroic pose as he does.

Patti Lupone makes an earthy sister who takes in her cop brother’s “witness” and his mother, Josef Summer puts a disarming, grandfatherly face on cunning cop corruption at the higher levels, Glover is pure menace and Czech actor Rubes pulls off stern, with a touch of humor, judgemental but wise.

Old Eli’s heartfelt lecture to young Samuel, who is fascinated with Book’s bravado and especially his service revolver, becomes a grace note for the ages.

“What you take into your hand, you take into your heart,” Eli warns, wary of the cult of the gun.

The Oscar-winning “Witness” became one of those cultural shorthand film phenomena of its day, with “You look plain” (a high Amish compliment) becoming a punchline and eventually the inspiration for a Weird Al Yankovich song and movie parody.

Weir, like other members of Australia’s 1970s “New Wave,” became “go-to” director, with the credits of a star filmmaker who had his pick of great projects to attempt.

The Juilliard-trained McGillis would follow up this film with the blockbuster “Top Gun,” and had a nice run of decent roles before interrupting her career for a second marriage that produced two children and a Key West restraurant infamous for its terrible service. Thankfully, she got back to acting.

“Witness” was and remains Harrison Ford’s best shot at an Oscar.

If The Academy gets its act together and serves up a much-deserved lifetime achievement award for him, “Witness” won’t be the only picture they show clips from, but it’s the best, a classic from a decade that produced as many of those as the much-more-praised 1970s.

Rating: R, violence, nudity, profanity

Cast: Harrison Ford, Kelly McGillis, Lukas Haas, Alexander Godunov, Jan Rubes, Patti Lupone, Brent Jennings, Josef Sommer and Danny Glover.

Credits: Directed by Peter Weir, scripted by Earl W. Wallace and William Kelley. A Paramount release on Pluto, Amazon, other streamers

Running time: 1:52