EVERY FRIDAY and Saturday nights, the entrances of hundreds of theaters across America are clogged with people who are there to see an obscure low-budget movie that features a mad scientist transvestite alien named after a hot dog (Dr. Frank N. Furter), a cryogenically-preserved '50s greaser (who escapes from his refrigerator and is, of course, hacked to death), an imitation Dr. Strangelove (who says things like, "This is, I presume, some kind of audio-vibratory molecular device"), and a narrator who has no neck. Besides a few of the uninitiated--called "virgins"--the audience has seen the movie one, two, five, ten or fifty times before, they have memorized all the lines, and added quite a few of their own; they throw rice and cards and toast and confetti and hot dogs and rolls of toilet paper, squirt water pistols and light candles (or shine flashlights, depending on fire regulations) at appropriate moments; they act the movie out on stage as it appears on screen. And now a sequel film, Shock Treatment, is in the works.

It is, in short, the stuff of which sociology theses are made.

But while the 1975 Lou Adler movie has sprouted a phenomenon in the United States, the original stage version has quietly hummed along in London since it opened in 1973. This month, Richard O'Brien's brainchild--he wrote the script, music and lyrics, and starred in the movie--began a nationwide U.S. tour with a two-week engagement at the Harvard Square. The Boston cadre of Rocky Horror fans seems to be greeting it with the respect and appreciation due the first draft of a recognized masterpiece--but not with the unmitigated love and devotion they display for the film each weekend at the Exeter St. Theater.

The only veteran from the movie is costume director Sue "Yay Sue!" Blaine. Frank Gregory undulates admirably as Frank N. Furter, but the image of Tim Curry's entrancingly seductive performance remains etched in memory as the real thing; Pendleton Brown plays a fine Riff Raff, Furter's alien sidekick--although his dark hair seems somehow un-Riff Raffish to those accustomed to O'Brien's bald-eagle blond cranium. Rocky fans, who recognize the slightest deviation from the standard film version, will perhaps cringe at each "revisionist" inflection or gesture; but, unless in a savage mood to begin with--distinctly possible given the overpriced tickets ($12.50, $15.00)--they should enjoy this competently acted and produced play, partly because of Rocky Horror's inherent bizarre charm, partly because of the shared in-joke it represents. Though little in the play is likely to diminish the movie in the eyes of true believers, some nice touches are evident. Stardust Memories actress C.J. Critt, as Columbia, Frank N. Furter's groupie, adds a freaked-out Haight Ashbury spaciness to her role; baton twirler champion Dennis Daniels portrays glistening muscle-god Rocky Horror, a Neanderthal in the film whose most eloquent line is "ugh!" with wit and gymnastic talent; and Steve Lincoln, as the narrator, hurries his lines, but the former ulcerridden CBS executive does well as the staid arm-chair commentator who occasionally trots into scenes to join the aliens and transvestites.

Frank Piegaro, sporting pipe, dark-rimmed glasses and an aura of klutziness, and the demurely attractive Marcia Mitzman, are well cast as the traditional innocent victims--the Denton, Ohio couplet of Brad "Asshole" Majors and Janet Weiss (as in "Vice".)

The decadence of Rocky Horror appeared to fit in well with the Harvard Square and its 1600 mostly dilapidated seats. Androgynous alien ushers prowled the aisles with flashlights before the show started, occasionally startling audience members and supplying just the right atmosphere of good-humored fright for a show O'Brien meant as a homage to the great science fiction chiller thrillers--the "B movies" of the '50s.

"Science Fiction/Double Feature"--sung at the beginning and end of the play by Trixie (Meghan Duffy) the usherette as she comes on to the back row while offering her buttered popcorn--recalls "The Day the Earth Stood Still" (Michael Rennie was ill"), "Day of the Triffids" (as in, "And I really got hot when I saw Janet Scott fight a triffid that spits poison and kills") and others, encapsulating this '70's retelling of Dr. Frankenstein.

TO THOSE who have never before experienced Rocky Horror but are willing to give it a chance, the best advice is not to worry too much about the bizarre if not always inteligible plot: the live rock music and the red-bulbed ersatz Radio City Music Hall set, and the hyperkinetic pace should suffice, at least for a start. Then check out the movie at Exeter. Those who bother to look past Rocky Horror's surface shock value--"give yourself over to absolute pleasure," urges Frank, "swim the warm waters of sins of the flesh"--will discover a literate and witty parody of the science fiction and horror genres that manages to remain unpretentious--though that hasn't prevented its legion of fans from adopting Rock Horror lifestyles based on Frank N. Furter's fundamental premise for existence: "Don't dream it, be it."

And if not converted by the evident attractiveness of a phenomenon that wavers between non sequitur and epiphany--epitaph?--for our times, you may find the "Time Warp" of socially redeeming value. Or maybe the ushers will scare you. Or--just possibly--there is no hope at all for you and you will end up like the student who, when asked what she thought of Rocky Horror, replied: 'Something that should be seen. Once."