It' 11:30 on a Saturday night in Georgetown.

Near the corner of Wisconsin and M. 300 people wait patiently, carrying bags of rice, newspapers, candles, cameras and deck of playing cards. Half a dozen are wearing white-face paint; their bloodshot eyes rimmed with charcoal. They are mostly highschool and college students, standing in line for the midnight screening of "The Rocky Horror Show," the tender story of a transvestite from Transylvania, now in its eighth week at the Key Theater. As the doors open, the line files past the box office to the tune of "White Punks on Dope" while the manager, wearing an arrow through his head, hands out kiddie birthday hats and noisemakers.

"This thing is growing every week," says theater manager Dave McGrew. "It's got a real hard-core following. Gays, couples, straights, crazy people. Areal fun crowd."

Initially released in 1975, "The Rocky Horror Show" was virtually ignored by critics and moviegoers. Rather than write it off, 20th Century Fox decided to give the film a second chance, hoping to attract the growing "midnight-circuit" crowd. They already had given their stamp of approval to low-budget, high-camp films like John Waters' "Pink Flamingos," Jamaican import "The Harder They Come," "Reefer Madness" and "Greaser's Palace."

Rocky Horror Show," directed by Jim Sharman from Richard O'Brien's original score, features British actor Tim Curry, in black-gartered pink regulia as the demented transvestite Dr. Frank N. Furter.His Frankenstein, a blond palooka named Rocky, is created to relieve the doctor's "tension," but not before a pair of Bobbsey Twins named Brad and Janet stumble upon the castle.

The horror show begins with a wedding scene: The audience joins in by pelting the screen with handfuls of rice. ("It's a touching experience," says one female patron, wearing black, ripped, fish-net stockings.) Three minutes later the groom proposes a toast. Pieces of toast come flying through the air. Flashbulbs pop. "SAY IT, SAY II" the crowd taunts. On cue, a character exclaims, "Great Scott!" One well-prepared fan tosses a roll of toilet paper down the aisle.

Caught in rainstorm. Brad and Janet (Susan Sarandon and Barry Bostwick) cover their heads with newspapers. Likewise the audience "There's a light . . ." the characters sing. Suddenly the theater flicks its collective Bic - candles, matches, lighters ignite. It looks like a human birthday cake and sounds like the Fourth of July - bells, noisemakers and a rousing self - congratulatory cheer as three women, suffering from boogie - fever, rush to the front of the theater for "The Time-Warp," a juvenile delinquent jitterbug. There's no letup. For two hours, the extras in the aisles respond to the movie with a Greek chorus of cheers, boos, hisses, hilarious comebacks and wise cracks, Example: (Movie) "Master, dinner is prepared." (Audience) "AND WE HELPED."

Explaining the movie's habit-forming appeal, Doug, a young man who has seen the film 25 times says, "It's a religious experience." He also belongs to the Rocky Horror Fan Club. "This is just like going to church. It's something to believe in."

"Rocky's" climb to cult status took exactly four years; from the time executive producer Lou Adler saw the original London stage version in 1974. Ten months later, Adler acquired world rights to the property and brought it to his theater in Los Angeles, the Roxy. The show was an underground hit on the coast, but later bombed in New York. "It ran three weeks," Adler recalls. "We tried to make it Broadway and it wasn't."

The film wasn't a first-run box-office smash either.

To save its investment 20th Century Fox stipulated that "Rocky Horror Show" be shown at midnight only in theaters with less than 500 seats. "That way," according to advertising executive Tim Deegan, "you have a good line out front. People in the cars passing by will say, 'Gee, that must be a terrific movie.' "Only 16 prints of the film were distributed and Deegan said his company was somewhat reluctant to replace old prints. "The scratchy prints does lend a certain aura," he says.

The 29-year-old Deegan, Fox's youngest advertising executive, takes credit for masterminding the cult, though producer Lou Adler isn't sure how it happened.

"I hated the film when I first saw it," Deegan recalls. "We spent no money on advertising. The strategy was to do absolutely nothing. It was deliberate calculation on my part."

Says Adler, "But that's not to say, 'Let's make a cult thing.' It's not that easy."

Deegan would not reveal box-office receipts so far, but said the film made for $1 million, has returned its initial investment.

"People say it looks smart in retrospect," says Adler, "but the truth is, Fox believed in the film." Reminded that Deegan disliked the film at first, Adler laughs. "That's right. But it doesn't mean he didn't believe in it."

As Deegan puts it, "I believe quite seriously that Amy Carter will be requesting this film at the White House - maybe even make the cover of Time magazine."

"The Rocky Horror Show" already has been banned in South Africa, caused near-riots in New York and last Month attracted 900 fans to a Rocky Horror Convention in Uniondale, N.Y., during the worst blizzard in the city's history. Last year, to celebrate the film's first -year anniversary at an Austin, Tex., theater, 20th Century-Fox flew Tim Curry over from England for a glittery reception attended by 1,500 people, most of whom were in costume.

Last month in New York, Greenwich Village storeowners near the Waverly Theater, which had been hosting "The Rocky Horror Show" for two years. complained the crowd was too wild. Fans of homosexual pursuasion were being taunted by beer-drinking "straights," and the merchants feared for ther windows. The Waverly hired a guard, but that wasn't enough. On Feb. 3, the film moved to the mid-town Festival Theater where business has dropped off considerably. ("Stupid booking," Deegan complains.)

Rocky's detractors argue that the so-called "cult" phenomenon was a commercialized one, that 20 Century-Fox hired a group of people ("The Rocky Horror Revue") to show up at theaters in costume. ("No comment," is Deegan's reply). And what about the suspicion that Fox's reverse-hype was just as slick as any Madison Avenue campaign/ "Maybe it's new Madison Avenue." the ad executive say. Tre executive producer says, "Now I guess it's calculated because it works."

The "Rocky" phenomenon prompted 20th Century-Fox to look through their vaults, searching for other midnight-circuit material. But as Deegan says, "If man could explain phenomenon, life would be pretty boring."