ROCK 'N' ROLL, the Frankenstein of 1950s American culture, conquered the world. Gospel, blues, R 'n' B, Country - all were jumbled up together and spit out in a kaleidoscopic mass of chrome hubcaps, leather jackets, slick haircuts and stiletto heels. The British invasion of 1964 might have stolen the show for awhile, but it was more of a new incarnation of the early rockers than an original product. By the mid-'70s, American business had taken over, and rock had become a $3-billion-a-year monster.

Last Sunday, however, there were villagers at the gate of the castle, and they had pitchforks and flaming torches . . .

They stood in a line that stretched for half a block on 2nd Avenue in front of New York's Entermedia Theatre - an odd, eclectic group of mostly young people, dressed in various stages of fashionable disrepair. Some darted into a nearby bar for a quick drink, while others stood by patiently, discussing the tonality of Schoenberg or the price of antique clothes. They paced about nervously in reserved anticipation.

Workers were still putting the finishing touches on the stage as the line filed into the theater. Microphones were checked, electrical cables secured. Slides flashed across the central projection screen, which was surrounded by an angular set painted in blarring colors that resembled microscopic photographs. The sound system poured out a steady torrent of abstract, dissonant music. When everyone was seated, the emcee, a balding, Bohemian sort, bounced across the stage. "Welcome to the Zu Mani-festival.!"

The crowd exploded, as the eerie, electronically-echoed voice of poet Jayne Bliss-Nodland drifted across the hall "Zu," a festival of alternative music, was finally a reality.

For the next 14 hours, the crowd of about 1,000 would be treated to and confronted by the music of some of Europe's leading experimental musicians (Daevid Allen, Chris Cutler, Fred Frith and Yochk'o Seffer) and various American groups who are embracing the new form of music as an alternative to the rock monster.

A week earlier, the scene in the spacious Chelsea loft of the festival's producer-provocateur, Giorgio Gomelsky, had left some doubts. Assistants were typing press releases, setting up equipment rentals and talking furiously on the phones. The recurring topic was money, or the lack of it. The European-musicians were having trouble procuring visas. An offer of recording equipment was being negotiated. A sense of controlled mania prevailed.

Hours later, in the midst of a conversation between several musicians, Gomelsky entered, with candles. He switched off the lights. "Ah, that's much more human."

He was soft-spoken, articulate, his English spiced with a heavy French accent. Yet an unmistakable air of portent pervaded his every move. He was like a time bomb, quietly ticking away, waiting to explode.

The "bomb" has exploded before, most notably in the early '60s when Gomelsky managed the then-fledgling Rolling Stones and later, the Yard-birds, with whom he produced the legendary "Rave Up" album. He is currently involved with the new generation of European experimental musicians who were featured at the festival.

"We call it the Zu Manifestival because "zu' was the messenger bird of Egyptian mythology and 'Manifestival' because it is also a manifesto - a statement of our beliefs about music and the artistic environment that creativity requires."

This music and its environment are in direct opposition to the traditional dominance of American musical ideas and the way in which the American record industry allegedly controls and manipulates foreign markets. The experimentalists have, for years, pursued a form of music that is a synthesis of various styles and folk idioms. They are attempting to create a new style that is international, as opposed to strictly American, in scope. Their music has as much in common with Stravinsky of Balinese gamelan orchestras as it does with Little Richard.

Playing this kind of music and confronting the American corporate colossus has produced problems. While many of the groups have gained a certain amount of notoriety in Europe, engagements and money are still scarce. French drummer Francois Laizeau was forced to play with a big band at the Moulin Rouge for a month to pay for his expenses at the festival. English musician Chris Cutler barely had the money for the air fare.

As a reaction to these difficulties several European avant-garde groups have formed Rock In Opposition (RIO), an organization that promotes the interaction and mutual assistance of experimental musicians.

The day before the festival, Gomelsky held a conference of the "alternative" media in the United States (mostly, representatives from small, independent music publications and college radio stations). The meeting resembled a small town political rally - everyone talking at once, working feverishly for no money and without expense accounts (some traveled from the West Coast). They are attempting to set up an organization similar to RIO which will aid musicians and bring attention to the music.

At the festival, there was a touch of irony in the performances of the American groups that opened the show. They were imitating their European heroes the way many Continental groups have adopted American styles for years.

Most of the early performances went from the ridiculous to the preposterous. One of the musicians slashed away at an electric guitar while yelling vocals that were unintelligible. Several groups wallowed in a thick mush of synthesizers. The crowd was polite and settled themselves for the European groups.

The festival began at 2 p.m., but the pace did not quicken until about 9 p.m., when two American groups - Robal, from New York, and the Muffins, from D.C. - both elicted a rousing response.

Robal featured cascades of guitar harmonics and languid lead lines set against a pulsating rhythmic accompaniment, while the music of the Muffins took various thematic leaps and turns that were engaging in their unpredictability.

When Hungarian-born saxophonist-panist Yochk'o Seffer and his group, Neffesh-Music, took the stage, the crowd began to boil with excitement. Seffer's music draws heavily from jazz, yet he adds a Slavic flavor that is similar to that of Bela Bartok. He is the archetypal European experimentalist - he freely fuses seemingly disparate sytles of music into a cohesive and intriguing musical entity.

Later, Chris Cutler and Fred Frith of the English group, Henry Cow, were featured in a brief set. "Cow," one of the foremost avant-garde ensembles, is noted for its eclecticism. Their music is frequently stark and dissonant and employs classical, jazz and rock motifs. Frith is a master of the electric guitar and has explored many of the sound capabilites of the instrument (he sometime "prepares" his guitar by attaching nuts, bolts and other foreign objects to the strings the way John Cage "prepares" his pianos).

The featured artist of the festival was Daevid Allen, co-founder of the two most famous experimental groups, Soft Machine and Gong. Allen and his wife Gilli Smyth performed with several American musicians who were dubbed, "New York Gong." They presented the first complete version of the Planet Gong Mythology, an extended work that captured the inspired dementia and playful spirit that characterized the original group.

While Allen scampered about the stage, directing the musicians, he was joined by a group of children, dressed as "Pot Head Pixies," who danced to the fast-paced rhythms and the delightfully disquieting blend of hard rock with Oriental and classical shadings.

At 4 a.m. Allen was still going strong when the theater owner literally pulled the plug. The crowd was already standing, and all of the workers and musicians of the Zu Manifestival joined him oustage while the drummers maintained a furious rhythum. The arc lights from a film crew illuminated a sea of ecstatic faces. Gomelsky was beaming. The crowd pressed close, in a moment of unbridled comradeship.

The metaphorical pitchforks shook angrily outside the castle of commercial rock, and the torches flamed very bright. The gates of the castle did not open, of course, but perhaps inside the monster heard, and perhaps, if only for a moment, was afraid.