PRINCETON, N.J. -- Sunday night, Oct. 30, 1938. America was listening to the radio, as always on a Sunday night, millions of families clustered around their gothic Zeniths with Magic Eye tuning ("No Stoop, No Squat, No Squint"). At 8 o'clock nearly all of them were tuned in to Charlie McCarthy, the insolent wooden companion of ventriloquist Edgar Bergen.

But on that night, just 50 years ago today, the nation was to get the Halloween eve scare of its life.

On 100 CBS stations, the Mercury Theatre of the Air announced its program, a dramatization of H.G. Wells' "War of the Worlds." Only 3.6 percent of the radio audience was listening, and not all started in time to hear Orson Welles' introduction, which went like this:

"We know now that in the early years of the 20th century this world was being watched closely by intelligences greater than man's ..." rumbled the familiar basso, setting the scene. "It was near the end of October. Business was better. The war scare was over ..."

As his voice faded, a weather report came up. And then, "We take you now to the Meridian Room in the Hotel Park Plaza in downtown New York, where you will be entertained by the music of Ramon Raquello and his orchestra."

After a few seconds of "La Comparsita," an announcer broke in.

"Ladies and gentlemen, we interrupt our program of dance music to bring you a special bulletin from the Intercontinental Radio News."

Americans had been hearing special bulletins for weeks. Hardly more than a month earlier, Britain and France had ordered partial mobilization against Hitler's Germany.

Now the doom-laden voice of news was speaking again. "At 20 minutes before 8, central time, Professor Farrell of the Mount Jennings Observatory, Chicago, Illinois, reports observing several explosions of incandescent gas, occurring at regular intervals on the planet Mars."

The voice quoted a "Professor Pierson" at Princeton and described "a jet of blue flame" rushing toward Earth.

Back to the music.

Soon another bulletin, an on-the-spot interview with Pierson: "This is Carl Phillips, speaking to you from the observatory at Princeton. I am standing in a large semicircular room, pitch black except for an oblong split in the ceiling ..."

It sounded like heads-up journalism. A few minutes later another flash:

"Now, nearer home, comes a special announcement from Trenton, New Jersey. It is reported that at 8:50 p.m. a huge, flaming object, believed to be a meteorite, fell on a farm in the neighborhood of Grovers Mill, New Jersey, 22 miles from Trenton. The flash in the sky was visible within a radius of several hundred miles and the noise of the impact was heard as far north as Elizabeth ..."

Slowly the story escalated. A mobile unit reported at the scene ("We take you now to Grovers Mill, New Jersey ...") to describe a giant cylinder half-buried in the ground.

"It has a diameter of ... what would you say, Professor Pierson?"

Pierson's voice, from the background: "About 30 yards."

A local farmer was interviewed -- "I seen a kinda greenish streak" -- as Carl Phillips drew a fantastic picture. "Hundreds of cars are parked in a field in back of us. Police are trying to rope off the roadway leading into the farm. But it's no use. They're breaking right through. Their headlights throw an enormous spot on the pit ..."

Suddenly his voice broke.

"Just a minute! Something's happening! Ladies and gentlemen, this is terrific! This end of the thing is beginning to flake off! The top is beginning to rotate like a screw! The thing must be hollow!"

The story got wilder and wilder. Shouts of awe from the crowd. "Good heavens, something's wriggling out of the shadow like a gray snake ... They look like tentacles to me. There, I can see the thing's body. It's large as a bear and it glistens like wet leather."

Now came another musical break, a piano this time. Then back to Phillips. "Ladies and gentlemen -- Am I on? -- Ladies and gentlemen, here I am, back of a stone wall ... What's that? There's a jet of flame springing from that mirror, and it leaps right at the advancing men. It strikes them head on! Good Lord, they're turning into flame! {Screams and unearthly shrieks here.} Now the whole field's caught fire. {Explosion here.} The woods -- the barns -- the gas tanks of automobiles -- it's spreading everywhere. It's coming this way. About 20 yards to my right ..."

Crash of microphone, then dead silence.

And a new announcer: "Ladies and gentlemen, due to circumstances beyond our control," and so on.

As the disaster metastasized, other voices were brought on -- "the commander of the state militia at Trenton," a network executive, an Army captain at the scene. Reports came in from Red Cross headquarters and the state police.

A huge metal device on legs, taller than the trees, attacked the militia with heat rays. Within minutes it had taken over central New Jersey.

"Communication lines are down from Pennsylvania to the Atlantic Ocean. Railroad tracks are torn and service from New York to Philadelphia discontinued except routing some of the trains through Allentown and Phoenixville. Highways to the north, south and west are clogged with frantic human traffic. Police and army reserves are unable to control the mad flight."

Finally "the secretary of the interior" spoke from Washington, urging calm. But more cylinders were dropping. New York ("I'm speaking from the roof of Broadcasting Building, New York City. The bells you hear are ringing to warn the people to evacuate the city ..."), Chicago, St. Louis.

And at last, as thousands raced for the East River, "falling like flies" in utter panic, fleeing clouds of deadly black smoke -- "now the smoke's crossing Sixth Avenue ... Fifth Avenue ... a hundred yards away ... it's 50 feet ... " -- the announcer broke off.

A lonely radio operator called plaintively, "2X2L calling CQ. 2X2L calling CQ. New York. Isn't there anyone on the air? Isn't there anyone? ..."

And silence. Dead air.

Six million people heard the broadcast. At least a million of them admitted they were frightened. Hundreds of thousands had tuned in to Charlie McCarthy, but at about 8:12, when Charlie's opening skit ended and a singer was introduced, they switched stations.

They picked up the story just at its most convincing part, before the science-fiction fantasy took off and after Welles' prologue.

Caught up in the rapidly developing events, people grew worried enough to phone the local police or newspaper -- but couldn't get through because the lines were jammed. To a jittery person looking out an apartment window, anything could appear to confirm the worst: noisy, honking traffic; a bad smell in the air; planes overhead.

Some listeners recognized Welles' voice; some sensed the phoniness of "Hotel Park Plaza" and "Intercontinental Radio News," names substituted for real New York names on orders from CBS; some noted the impossibly compressed time frame and knew it couldn't be real. In the program Phillips says he and the professor got from Princeton to Grovers Mill in 10 minutes, which is pretty good in itself. But in fact it took barely one minute of real time.

As actor John Houseman tells it in "Run-Through," his readable and useful autobiography, "Our actual broadcasting time, from the first mention of the meteorites to the fall of New York City, was less than 40 minutes. During that time men traveled long distances, large bodies of troops were mobilized, cabinet meetings were held, savage battles were fought on land and in the air."

Houseman, who was president of Mercury Theatre, says the cast was having trouble with the show, which was a last-minute substitute for a period drama, but that "under Orson's hands a strange fever seemed to invade the studio -- part childish mischief, part professional zeal."

The actor playing announcer Phillips modeled his role after the classic reporting of the Hindenburg zeppelin disaster, with the near-hysterical voice, the stunned pauses, the asides: "Get this, Charlie! Get this, Charlie!" Surely the memory of that famous broadcast reverberated in many minds, adding authenticity by association.

And the device of the studio music between bulletins was, Houseman says, a masterstroke. "Tension -- release -- then renewed tension. Soon after that came an eyewitness account of the fatal battle of the Watchung Hills; then, once again, that lone piano was heard -- now a symbol of terror, shattering the dead air with its ominous tinkle ... That piano was the neatest trick of the show -- a fine specimen of the theatrical 'retard,' boldly conceived and exploited to the full."

Whatever it was, "War of the Worlds" gave America its first -- and worst -- case of media-triggered anxiety.

Farmers who lived around Grovers Mill packed their families into cars and drove -- to Trenton, to Pennsylvania, to the nearest woods (a curious instinct; do we at bottom mistrust our own civilization?). The fleeing met the incoming traffic of the curious, and soon all roads in the area were clogged.

A famous news photo, widely published the next day, showed New Jersey farmer Willie Dock, 76, standing with his pipe and his rifle by a barricade of grain sacks. A water tower at Grovers Mill was riddled by gunfire in the night.

According to a Page 1 story in The New York Times, more than 20 families on a single block of Hawthorne Avenue in Newark "rushed out of their houses with wet handkerchiefs and towels over their faces to flee from what they believed to be a gas raid. Some began moving household furniture ..."

All over New York City, families fled to their cellars or attics or to neighborhood parks. Hundreds of citizens showed up at police stations, asking to be evacuated or screaming that the city was being bombed. Thousands called newspapers and police stations, usually getting little satisfaction until the Associated Press began transmitting an explanation at 8:48 p.m.

Somebody called The Times to ask if it was the end of the world. The reply has not come down to us.

People crowded into the streets and onto roofs to look for signs of an air battle. Church services turned into prayer sessions for protection in Armageddon. Doctors and nurses called Newark police to offer their services to the victims. A Newark hospital treated 15 people for shock and hysteria.

In Bergen County, N.J., a power brownout added to the excitement, causing another flood of phone calls. Scores of motorists called police to find out how traffic was being rerouted from the "destroyed" Pulaski Skyway. And when the program mentioned that 7,000 National Guardsmen were being mobilized, hundreds more calls overwhelmed armories and recruiting offices.

The Washington Post missed the story completely on Monday but reported it Tuesday, including the news that "hard-boiled United States Marines wept and prayed in their barracks at Quantico, Va., in the wave of terror ..."

Callers, hysterical, baffled or resolute, were reported in San Francisco, Chicago, St. Louis, New Orleans, Baltimore, Providence, Boston, Kansas City, Birmingham and Indianapolis. "My God," one man shouted, "where can I volunteer? We've got to stop this..." Houseman writes that even as the program ended, after a second act that "nobody heard," the studio phones rang and the mayor of a big Midwestern city came on screaming for Welles' hide. "Choking with fury, he reported mobs in the streets of his city, women and children huddled in the churches, violence and looting ... I hung up quickly."

The furor went on for weeks, with nearly a million prewar dollars in lawsuits filed against Welles and CBS, "for damages, injuries, miscarriages and distresses of various kinds -- not one was substantiated," Houseman adds. CBS apologized, though it did point out that the broadcast had been previously publicized and was described as fictional not only at the outset but five more times during the evening.

In 1947 "The Invasion From Mars: A Study in the Psychology of Panic" by Hadley Cantril was published by Princeton. Through interviews with 135 "survivors," it isolated various criteria for suggestibility and, more to the point, nationwide panic. Among them: education levels and such coincidental elements as the international tensions of 1938 and the long, stressful years of the Depression just ending.

There was a "ground zero" mentality, with the fear generally lessening with distance from Grovers Mill. There was in some a tendency to discount events that the listener knew could not be happening, in some others a tendency to override that skepticism. There was the business of the dial-hoppers: Only 12 percent of the interviewees listened from the beginning and still believed it. Forty-two percent said they had tuned in late.

In a separate CBS survey of 920 people, the book reported, "175 thought the broadcast was news and of these 24 learned the real nature of the broadcast by coincidence or by the checks of others."

The book concludes:

"It is not the radio, the movies, the press or 'propaganda' which, in themselves, really create wars and panics. It is the discrepancy between the whole superstructure of economic, social and political practices and belief, and the basic and derived needs of individuals that creates wars, panics or mass movements of any kind. And human needs can only be curbed by the deliberate and forceful cultivation of ignorance, intolerance and abstention."

This year Oct. 30 again happens to fall on a Sunday, and "War of the Worlds" will be fought anew on National Public Radio (in Washington, at 6 tonight on WETA/FM91). The updated anniversary remake, originated by station WGBH-FM, Boston, and picked up by 150 other NPR stations, has been recorded with state-of-the-art radio equipment outdoors at filmmaker George Lucas' Skywalker Ranch. It will feature the voices of Jason Robards, Steve Allen, Rene Auberjonois, retired newsman Douglas Edwards and others.

There will be plenty of disclaimers, says director David Ossman.

The original broadcast can be heard at 8 tonight at the Air and Space Museum's Albert Einstein Planetarium. And the National Portrait Gallery has opened a major show called "On the Air: Pioneers of American Broadcasting," covering radio and TV history from Marconi to the 1960 Kennedy-Nixon debates. The original working script of "War of the Worlds" is on display.

Incidentally, the end of the story, which everyone missed in the uproar, comes when the invaders are destroyed, not by weapons but by germs -- "the humblest thing that God in His wisdom put upon this earth," as the script says.

Today, Grovers Mill is a high-priced housing development. The grist mill itself, built during the Revolution by George Bergen and named by another owner, Joseph Grover, in 1859, still stands, a rambling gray building with some old millstones decorating the corners.

Grovers Mill Graphics occupies the place, but out back, above the stagnant millrace, ancient rusting gearwheels set in rotting hand-hewn beams can still be seen. The millpond across the street is at the moment a dried-up swamp full of cattails.

There are those who say that this, Orson Welles' greatest magic trick, could never be duplicated, that modern audiences are too sophisticated, too accustomed to fantasy on their screens, and that the problem today would be to convince the public that an actual disaster of such scope was real.

"Sophisticated? I don't care if we are," says Sheldon Judson, a retired Princeton geologist who rode out to a Grover's Mill himself that night. "It could happen again."