THEY HAD THIS IDEA that if Bud Cort got dressed up in the Nazi SS colonel’s uniform and walked around the Marienplatz at lunchtime, people would freak out en masse and it would be like getting a lot of extras to work free.

But most of the Christmas shoppers and commuters in Munich’s main square just ignored Cort’s black-white-and-scarlet swastika armband, gave him about the same polite notice that meter maids get.

One woman, making the classic home movie of relatives standing rigid and smiling with something scenic in the background. politely lowered her camera as he started to cross her field of vision. She smiled and wished him a guten Tag. He returned her greeting, saluting with his riding crop.

Cort — who was Pvt. Boone in M*A*S*H and whose first big starring role was in the award-winning Harold and Maude — has the title role in a new German-American movie called Hitler’s Son.

"It could be another M*A*S*H," asserted Cort a bit defensively when I suggested the basic idea of the film seemed a little thin.

The story line is fairly simple: Hitler and Eva Braun had a son (not to be confused with that fellow they found in France). As a baby young Willy Hitler was sent high into the Alps to be brought up by a loyal retainer, an SS colonel who told him nothing about his past or parentage.

When the old man dies, the illiterate Willy, now 33 and decked out in Bavarian shepherd-boy gear, makes a trip down from the isolation of his mountains to see about collecting a war orphans’ pension. The fun begins when the postmaster reads the birth certificate and tells him to take his troubles to Munich (Willy takes along his foster parent’s old uniform) .

Horror movie veteran and Star Wars super-villain Peter Cushing plays Heinrich Haussner, leader of a neo-Nazi sect that finds out about young Hitler and claims him as its own.

But Willy, who has known as little of women as of towns, is a disappointing boy Führer. He is more interested in his first love, played by 22-year-old British starlet Felicity Dean, than in fascist posturings. And so it goes, with chase scenes and love scenes and bittersweet ends.

The screenplay was written by Lukas Heller, who scripted The Dirty Dozen, The Killing Of Sister George and Whatever Happened to Baby Jane? Co-author Burkhard Driest, a German author and actor, who served five years in prison for robbing a bank shortly before he was to graduate from law school, came up with the idea. Driest plays a small part in the film.

Hitler’s Son was shot in Bavaria — in Munich and in the village of Sachrang, about an hour’s drive southeast of the city, perched on the border near Kufstein, Austria.

A half moon hung low in a deep blue sky splotched with wispy clouds as we drove up to Sachrang with Vancouver-born Ruth Cameron, an attractive actress and would-be movie star.

Between acting jobs she was working as an assistant to Hitler’s Son publicist Al Hix (yes, he writes those cryptic letters to the editor of the International Herald-Tribune). As we climbed the snowy valley road, Cameron pointed out the old palace in Aschau which did duty as a mental asylum in the movie. Perched on a craggy promontory, its high, smooth walls and tiny, forbidding windows made it a natural for the part.

She told us about Cort’s driver, who had totalled a Citroen limousine the day before when he hit a deer between Aschau and Sachrang. Bud, she figured, was probably still upset about it and might be hard to interview, although he had not been in the car at the time. I kept my eyes on the road as we speculated on the prerogatives and foibles of movie stars.

The tiny Chiemgau village of Sachrang has long been a favorite tourist spot, crammed with cross-country skiers in the winter, booked solid six months in advance for the summer season.

Straddling a snow-fed brook in an Alpine meadow, Sachrang has survived intact as wars swirled around it for centuries. The half-timbered houses seem to have been peeled off a Bavarian postcard, with creamy white stucco exterior walls, wooden balconies, painted flourishes above the shuttered windows, every spare room for rent by the night or by the season.

Many of the houses have barns attached containing slightly fragrant, occasionally lowing cattle. There aren’t many such villages left.

Since the Munich film and TV industry discovered it a couple of years ago, Sachrang has been in a state of almost continual friendly occupation.

The farmer’s huts perched on the towering foothills above Sachrang would be just right for Alpine tales of the Heidi variety; the valley below provided the perfect backwater village required for the emergence of Willy Hitler.

The villagers don’t even stare any more at spectacles like Anna Neumeir’s general store under siege by technicians aiming floodlights through the windows to simulate sunlight, since during most of the abbreviated winter days Sachrang lies in deep shadows cast by those foothills.

The little shop had been outfitted as a post office by a quiet, usually-smiling German named Herbert Strabel, who picked up an Oscar a few years back for sets he designed in Cabaret.

Neumeir’s store, small to begin with, was jammed with Strabel’s set and with cameras, actors and director Rod Amateau.

Everyone not directly involved in the scene stood in the cold front hall of the old building or just outside the door, where a false mailbox and stamp-dispensing machine were mounted as part of the set. Every now and then a Sachranger or tourist would drop a letter in one or money in the other.

A little girl came to buy a can of soup for her mother and was sent 30 yards away in minor confusion to the only other store in town, which was doing an excellent business.

One of the people standing in the snow and the crystal alpine air, sipping Glühwein and trying to bask in the thin midday sunshine was American character actor Leo Gordon, a big, burly fellow with a craggy face who, even outdoors, looks like he needs more room to move around.

Gordon, who plays the role of Heinrich Haussner’s bodyguard and spare wheel, took an interview break on his way to lunch after the morning’s shooting; he and Cushing had spent the last hour or so storming in and out, in and out of Anna Neumeir’s store demanding over and over again of the "postmaster" where Willy Hitler could be found.

Gordon, with some 300 television scripts to his credit, speaks in the short, to-the-point sort of sentences used on TV. "I usually play heavies," he said. "This is the first comedy part I’ve had in years.

"Working with Peter Cushing is beautiful — we come over like an aged pair of Laurel and Hardy types, reversed of course. It’s out and out comedy. It’s a ball. It’s fun. I think it’s got all the qualities of M*A*S*H. It’s the kind of a kitsch picture that will appeal to the younger people."

On the Hollywood scene since he was 15, Gordon spends more time writing than acting these days.

"Most of my stuff has been Western heavies. The Western faded out, so I turned to the typewriter. Most of the stuff I write is adventure stuff. I just finished doing a script for Baa Baa Black Sheep. I’ve written 21 Adam-12 shows."

I pushed one of his buttons when I asked him about the relationship between the police shows he has written for and the real world of police work.

He said he goes for realism. "I’ve flown in the police choppers and watched how they operate ... been on homicide calls. Mod Squad and The Rookies are jokes. Police Story, Adam 12, the old Dragnet are the real thing. Compressed, of course."

If the apparent philosophy behind some of the cop shows is that you should bust heads first and ask questions later, maybe part of it is rooted in Gordon’s view of the nature of the law and the place of violence on the screen:

"Some of the laws they’ve passed now — they see an obvious vagrant there’s nothing they can do about it.

"The most violent, blood and gore television in the world is in Japan. But the crime rate is low because the Japanese know how to deal with criminals. The bleeding hearts say, `He’s an armed robber and a mugger because he wasn’t potty trained right.’ I say, `Blow him away.’ "

The big news from Gordon’s California home that day was of the L.A. Strangler, terrorizing much of Los Angeles. "When they catch the S.O.B. he should be drawn and quartered," he said sternly, adding he doubted anything so drastic would emerge from the criminal justice system. "I like Mexico. When you screw around with somebody down there he doesn’t go to the law."

He praised the unpleasantness of prison life in France, and the absence of parole in that country: "France has a recidivism rate of two per cent. Ours is 65. We have luxury in San Quentin — color TV sets in the cell. In France when you get out you don’t want to come back."

Gordon suggested the Mongol warrior Genghis Khan as a good model for students of public administration: "Genghis Khan ruled half the world — it was the boast of his court that the most beautiful girl in his kingdom could walk the length of the kingdom and not be molested."

In America — lacking the will to deal properly with criminals — he said, "there seems to be a trend toward gratuitous violence for the sake of violence.

"I know an American that lives here in Europe now. He was living in Los Angeles and he came out of his house one night and saw these two beatnik-looking characters who had guns up against this guy’s head. He looked at that and said, `Hey this is where I live. The hell with this noise.’ He left five years ago.

Start teaching them young, says Gordon: "Young kids — it sounds archaic, but you have to kick their asses. I think people have been degutted."

DURING the afternoon shooting, director Amateau wasn’t satisfied with the fighting on the scene. While he rearranged the artificial sunshine, professional bad guy Peter Cushing found time for a smoke and a chat.

Cushing, impeccably polite, wits an aura of studied dignity about him, neatly policed up the old butts lying in the hall before lighting his English cigarette, then proceeded to flick his ashes on the floor. He was tired after two months of shooting on location, eager to be finished. "I prefer working on a set," se said. "I think people always think they’re sets anyway." But he was excited about the film.

Can a movie about Nazis be funny? Absolutely, says Cushing. "Arsenic And Old Lace is rather terrifying theme, but it was one of the most hilarious pictures that ever been made. It’s just a comedy that comes out of this situation."

Cushing got his first real film role in 1939, in The Man In The Iron Mask starring Louis Hayward. He logged a long string of professional TV and film credits, and wandered into horror films in the fifties.

He found himself a star there for 10 years in films like The Mummy, Scream And Scream Again and The House That Dripped Blood. "It was one of those things that happened. The first one was such a success, Frankenstein in 1956 I think it was ... This was the first one of its kind, a remake of the 1939 film." The work was steady and interesting.

And then there was Star Wars. Cushing played the Grand Moff Tarkin, master villain in the smash hit space opera.

"Star Wars surprised everybody," he recalled a little wistfully of the film where he had chosen to work on a straight salary rather than for a percentage. "I think it’s a picture that will be shown every year like Gone With The Wind. What is so refreshing about it is it’s a real family film. Anyone can go to see it."

Star Wars was different in the making, too. "Lots of the scenes we just played to a blank screen. That was a rather strange experience. Not seeing what you were talking about."

He refused to speculate on the commercial fate of Hitler’s Son, saying only that the film would probably be made or broken in the cutting room, but that the editors would have some good footage to work with.

"Yes, it could be another Star Wars — audiences are so unpredictable, it’s very, very difficult to tell. This is the sort of picture that will be sold by word of mouth. As far as an actor and director are concerned, you just try to make the best picture you can."

A lot of Britons have become voluntary exiles to California, the Isle of Man, and other climes to escape the high rate of British taxation.

But not Cushing. "I love England," he said, a little shocked at the suggestion of living in L.A. "I wouldn’t live anywhere else but England."

At the end of the last day of shooting, Rod Amateau — and most of the rest of the company — came to dinner in the only restaurant in Sachrang.

The director had made it through the 56 days of filming in spite of a chain of mishaps that included a broken finger and two eye operations.

New York-born Amateau, who now lives in Rome, was a stunt coordinator and a writer before becoming a television and movie director.

His high-energy directing style developed in the pressure-cooker of weekly television, where he cut his teeth in the pioneering days of TV — The Burns and Allen Show, Playhouse Of The Stars. Nibbling one of his last Bavarian dinners for a while, he talked about television and movies and architecture.

"In motion pictures you get a moth’s-eye view of the action. In a motion picture theatre the chair is bolted to the floor. Your focus is on that area ahead of you. The people are bigger than life. They seem godlike and more important." He began to fill up my notebook with stick men and stick buildings.

"Public buildings in America are built on a human scale, one-to-one," he said. Then, drawing a picture of a small man standing by a gigantic building: "Italian public buildings are scaled 12/8 of life size. They are bigger than life." What about television, then?

"I don’t think television will ever replace motion pictures. Television doesn’t move. Television is a cheat on the movie. It’s a hybrid. Television people are physically and metaphysically smaller."

Which is not to say that people who work in television are somehow less professional than movie and legit stage actors. "Mary Tyler Moore and Carroll O’Connor do every week what Brando does once every two years and gets an award for," Amateau snorted.

He got involved in seeing if he’d missed anything on the now too-familiar menu as Bud Cort strode in wearing a silvery jacket styled after the astronauts’ deep space lounging wardrobe, big round sunglasses popping out from under an oversized cap.

Cort made clear from the first that he wasn’t interested in discussing his home life. "My private life is very valuable to me," he said. He would only reveal that he fries his eggs in peanut butter (not the crunchy kind). "You should try it."

Cort on the surface was calm, tired as everyone else, yet there was an air of controlled insanity about him, high intelligence mixed with lurking instability, as though his excellent Harold in Harold and Maude was just Bud Cort being himself with his defenses down.

He routinely turns down work that disagrees with his political and professional ideas.

"I was offered more for five Toyota commercials than for every film I’ve made put together" — he says he turned it down because it was too crass and exploitative. "I’m in no hurry to be rich — the only good thing is it keeps you out of the old welfare line."

He also declines most television work, particularly series offers. "You can’t really give a solid performance. It takes some of the magic away if you’re on TV every week."

He is still on the big screen every week, though. He said every print of Harold and Maude is in circulation.

Cort jumped at Hitler’s Son. At its roots the film is a stab at the Nazi credo of racist hatred that cost so many lives in the 1930s and 1940s. "My father was a second lieutenant in World War II — he helped liberate Dachau. He used to wake up screaming."

Cort was carrying a small pillbox his father had liberated in 1945 from the furnishings of Hitler’s "Eagle’s Nest" hideaway, atop a mountain near Berchtesgaden.

Handling the relic of the Third Reich, said Cort, helped him keep his focus in making the film.

"I’ve always been interested in genetics. This is a movie about genetics. I think it’s going to be a very important movie."