Disco is either a new religion or the revival of a very old one - the Bacchanalia with a beat.

That is the impression left by the many extravagant claims made on behalf of the growing disco dance craze, an acknowledged social and business phenomenon, at a four-day disco convention here which would up last night.

Sponsored by Billboard magazine, the record publication, the fourth annual Disco Forum attracted about 1,500 discotheque owners, disc jockeys (or "spinners" as the prefer to be called), and purveyors of what are supposedly the latest trends in disco lightin, sonics, fashion and music.

It also attracted some of the most popular disco performers, the Trammps, Tavares, Chic, Village People, Andy Gibb and Donna Summer who, seeking the promotional exposure, played at the behest of their record labels.

AT its finish, one was tempted to ask the question sported on one of the T-shirts worn here - "Is there life after disco?"

The hyperbole began with a press kick-off luncheon where Billboard's Bill Wardlow, a graying, middle-aged man who likes to be called "Father Disco" and who organized the event, kept referring to disco as "a whole new way of life.

"Disco is not just a place where people take drugs, get bombed and do other exciting things," said Wardlow. "Discotheques will be the dance halls of the future," he said, not to speak of the present.

He put the disco "industry" at $4 that in the future, disco "is what the ward $10 billion." That would make it bigger than the record business and the movie business combined.

Neil Bogart, the president of Casablanca Records, which has become one of the major record labels in just a few years on the basis of disco recordings of artists such as Donna Summer and the Salsoul Orchestra, gave the keynote address and said disco was "a rediscovery of American's greatest byproduct - fun.

"Disco has swept around the world with a force not seen since the early days of rock and roll," he said, adding that in the future, disco "is what the history books will inevitably call a revolution. And as revolutionaries, remember one thing - keep it fun."

Mayor Edward Koch also officially designated last week as "disco dance week" in New York City.

A proclamation said "disco and its lifestyle have helped to contribute to a more harmonious fellowship towards all creeds and races.

"The beat of the disco is the heartbeat of what makes New York City a special kind of place - vitality, individuality and creativity," it continued. "People all across America made the discotheque popular - New York City made it a phenomenon."

That the disco is a '70s phenomenon is indisputable. It has done more to revive nightclubs and dancing than anything since the big band era and the 1940s when - in the words of Cole Porter - the crowds at El Morocco punished the parquet.

Once moribund dance schools have had a revival as people yearn to learn to hustle like John Travolta.

It has spawned a series of extravagant dance palaces like Studio 54 in New York and The Plum and Pier Nine in Washington, which draw big crowds nightly with their swirling lights, throbbing music and the opportunity for glittering self-display.

An outgrowth of the twist bars and dance clubs of the 1960s, discos emerged distinctively in the mid-1970s as gathering places primarily for gays and blacks.

From there its chic spread to the white and straight communities, and from the cities to the suburbs.

But it took the movie "Saturday Night Fever," and its best-selling soundtrack album to catapult disco into the ranks of big, big business.

A modestly budgeted movie about the drab life of a Brooklyn youth whose only outlet for escape is the dance floor of the local discotheque on weekends, the film has already grossed well over $100 million and made John Travolta a worldwide superstar.

The two-record album featuring the Bee Gees has become the biggest-selling record in history. Still topping the record charts after 30 weeks, 15 million copies have been sold worldwide, and projections are now that sales will easily surpass 20 million copies.

As estimated 10,000 discos are now open around the country, lured by the prospects of the potential big payoff of places like Studio 54, the queen of discotheques whose initial $500,000 investment was earned back by its owners in a matter of months.

But the failure rate can also be high, and the need to keep coming up with more and more spectacular settings to attract the crowd has put the start-up costs for the big-city discos above the $1 million mark now.

"In New York you can make a small fortune very fast, but the place won't last very long, while in other places you might not make a small fortune, but it will last longer," said Frank Cashman, a convention attendee who owns eight smaller discos.

Xenon, a new disco which hosted many of the entertainment events at the convention and is trying to displace Studio 54, has supposedly sunk $2 million into its interior. It is a converted Broadway theater that includes a descending light apparatus that is supposed to look like the flying saucer in "Close Encounters of the Third Kind."

But most of the convention participants seemed unimpressed by Xenon, and because of its limited dancing space it is being dubbed Studio 27.

Steve Rubell, the shrewd owner of Studio 54 who knows there is no better way to attract the fashionable crowd in New York than by keeping people out, spurned Billboard's offer to hold the Disco Forum event sat his spot.

"No I don't want the thousands in here, and I don't have that much to gain by going," he said. While the disco acts were appearing at Xenon, Studio 54 on Friday night was hosting a benefit party for Martha Graham and her dance company.

Studio 54 is where Liza Minnelli does her almost nightly act after "The Act," her Broadway show, is over, and where even Vladimir Horowitz can be spotted - if you can get in. The general public, with few exceptions, is excluded, and so are some card-carrying members of Studio 54, which has occassioned a number of lawsuits.

"We turned away the president of Cyprus because he looked boring," said Rubell. Meanwhile, he said, the disco business is "booming, booming, booming" but "more people are going to lose money in the disco business because Studio 54 is such a success."

At the disco forum, Washington's Michael O'Harro, who runs Tramp's in Georgetown and who was "disco consultant of the year" in 1975 and 1976, was much in evidence - bearing his own publicity kit.

"Disco is almost becoming a religious experience," said the enthusiastic O'Harro. "It touches all emotions and senses - it is a revival of chic." O'Harro said he was trying to found a Washington-based disco trade association, "but I find a great reluctance among disco owners to share ideas."

There was even an academic on the official program - professor Richard A. Peterson of Vanderbilt University, who spoke of the sociological significance of disco. He said it was a chance for people with routinized 9-to-5 lives "to be different."

At a disco, he said, "you can walk, you can spend, you can dress, you can look like you're important," which is important if you're not. "The important thing is to walk in like you own the place," he said.

Peterson, who has written a book called "The Second of Social Change," likened the disco boom to the significance of jazz in the 1920s and rock in the 1950s as societal breakthroughs.

He also claimed that while "jazz was the coming out of blacks for the urban American consciousness, "disco represents the emergence of and coming out of gays." In disco, "the image leaders and the style setters tend to be gay."

While the Disco Forum included a variety of working seminars on all aspects of the business, many of those in attendance seemed most interested in finding which hotel suites various record companies were located in so they could get free samples of their records.

"Most of the people here are vinyl freaks and are mainly here to get records," said one participant.

One of the more unusual record companies represented here was House Top Records, a division of the Christian Broadcasting Network, which had previously specialized in gospel music.

House Top was pushing its first disco album, Theme from Judas, a 10-song "Suite," and was particularly promoting the song. "Thirty Pieces of Silver."

Allen Rundel of House Top said his company found no inconsistency between its religious orientation and the sensate disco world.

"The perfect place for our music is in the discos," said Rundel, "and if Jesus were here in our lifetime, he would go to the discotheques."