Fifty years ago next month, America’s obsession with UFOs blasted off with the stunning Air Force announcement that a crashed flying saucer had been found in the desert near Roswell, N.M.

Though the military started backtracking within hours, concocting a cover story - recently acknowledged to be phony - that it was just a weather balloon, the little green men had invaded the public consciousness and were here to stay.

Over the past five decades, the UFO craze of the summer of ‘47 has grown into a vast and complex subculture. And in the past five years it has exploded on the Internet, where “abductees” commune with “researchers” and do battle with professional skeptics.

But the town of Roswell remains ground zero. The first X-File. The granddaddy of all close encounters.

The desert retirement town located miles from anywhere, mostly forgotten until the city fathers decided to hop on the UFO bandwagon a few years ago, has become a mecca for thousands of saucer-eyed pilgrims.

On July 1, as many as 100,000 UFO devotees are expected to descend on sleepy Roswell for a wild, weeklong festival celebrating the golden anniversary of the still mysterious Roswell Incident that started it all.

Twenty TV satellite trucks are already there, and scalpers are hawking long-soldout $38 motel rooms for $200 and up.

There will be a UFO film festival, a golf tourney, laser shows, a concert, lectures by abductees, a costume parade, an Alien Chase 10K run - and lots and lots of goofy merchandise.

Like a sweater knitted from wool sheared from sheep that graze at the crash site ($225). Or vials of “certified, authentic soil direct from the UFO crash site, some possibly containing minute fragments of the object that plummeted to Earth” ($19.95). Or alien-shaped lollipops that actually emit light ($1.75).

Also on hand will be retired Army Col. Philip Corso, who just wrote a book saying alien technology harvested from the Roswell saucer wreckage led directly to the development of lasers, fiber optics and the microchip.

Corso - the highest-ranking military official to promote the UFO story - says he ran a Pentagon program that funneled knowledge gathered from the debris to defense contractors.

His credibility took a knock when Sen. Strom Thurmond accused Corso of tricking him into writing a forward by pretending the book would be a simple autobiography, not a UFO conspiracy book.

Roswell Mayor Tom Jennings insists there’s nothing at all odd about the legions of UFO devotees who have already started arriving for the July 1-6 shindig.

“These people aren’t weird. These people are family people. These people are all-American: apple pie and UFOs, man,” he said.

For Roswell’s 50,000 residents, little green men have translated into big green bills.

Families making the trip specially to see Saucer City, U.S.A., bring in about $5 million a year, according to Forbes magazine.

They stay in roadside motels and browse through the racks of Impact Site T-shirts hanging in the local Wal-Mart.

They visit the two dueling UFO museums and pay $15 for a bumpy bus ride into the desert. There they goggle at the small American flag fluttering in a gulch by a limestone cliff.

That’s the spot where something crashed during a storm July 2, 1947, spreading metallic debris over about three-quarters of a desolate mile.

The local sheriff called the Roswell Army Air Field, which sent Air Force intelligence officer Jesse Marcel out to take a look.

Years later, Marcel described the wreckage as being very lightweight but extraordinarily tough. There were unbreakable sticks painted with lavender hieroglyphs and lots of what looked like tin foil, which could not be torn, creased or burned. When crumpled, the tin foil unfolded itself, he said.

On July 8, the base commander issued what has become one of the most famous press releases of all time.

“The many rumors regarding the flying disc became a reality yesterday,” it said, explaining that the Air Force had found a flying saucer.

That afternoon, the Air Force called a press conference to say the flying saucer was just an ordinary weather balloon. Marcel posed for pictures beside remnants of a weather balloon.

But in 1979, ridden with cancer, Marcel went public to say he knew darn well what a weather balloon looked like and never would have mistaken one for a UFO. He said he went along with the cover-up to keep his job.

In a slew of books published in the early ‘80s, his son, Jesse Jr., now a doctor in Montana, and dozens of other witnesses described handling the same weird tin foil and unbreakable sticks with indecipherable violet lettering.

Unfortunately, not even one shred of unfolding tin foil exists to support the story.

The Roswell folklore grew over the years to include not only wreckage, but four or five dead alien bodies that the government supposedly keeps at a secret Nevada base called Area 51. That story has become such a pop culture staple that it was the key plot point in last year’s blockbuster “Independence Day.”

Then, in 1994, the Air Force released an entertainingly sarcastic report on what really happened at Roswell.

The weather balloon story was a fake, the Air Force admitted. What crashed was a top secret, balloon-borne radar reflector called Project Mogul that was supposed to detect whether the Soviets had exploded an atomic bomb.

The Air Force added dryly that if the military couldn’t keep atomic secrets from the Soviets, it certainly couldn’t have kept captured aliens under wraps all these years.

But most UFOlogists easily dismissed the report as a new, improved whitewash. It didn’t help when the General Accounting Office said the Roswell base records from 1946 to 1950 were missing.

Graphic: Roswell, New Mexico anniversary