It was a mob scene, with all the flash and cash of the 1970s.

By the time the doors opened Tuesday night at Studio 54, a new disco built into a cavernous former television studio, easily 100 limousiness were inching from Eight Avenue east on 54th Street and more that 1,000 colorfully dressed men and women were crushing against the entrance. Almost as many again pressed to get in at the back of the building.

Eight thousand invitations went out along with a network of phone calls to "a good social list," as a public relations pro called it, meaning the likes of Cher, Tennessee Williams and Margaux Hemingway.

They all came, as did Williams' goddaughter Natasha Grenfell, her mother, Lady Maria St. Just, and director Bert Shevelove, who arrived with Williams, plus the queen of Spain's grandson Prince Marino Terelino y Borbon, American couturiere Charles James, young menswear designer Jeff Banks and about 50 performers from Ringling Brothers circus.

About 4,000 in all got in, but the overflow easily numbered a thousand, good subjects for paparrazzi who never got near the front door. New York magazine editor James Brady, Warren Beatty and, if you believe the flacks, Frank Sinatra and his wife gave up after seeing the crush.

Some in the crowd wore down suits, others added a touch of gold or silver, and still others were a mix of nostalgia, three-piece business suits, Left Bank superchic and underground disco super casual.

Billed as the Fortunte Gallo OPera House in 1927, the Studio 54 building later became the New Yorker Theater, defaulted into the Casino de Paree, and then a Federal Project theater, before being bought by CBS as a television and radio sound studio in 1943. It was the setting for "Your Hit Parade," Jack Benny, "What's My Line" and "The $64,000 Question," as well as other top programming in its day.

The club is touted to have cost $1.1 million to refurbish and decorate and it could be so. It has its money roots in the Borough of Queens, where co-owners Stephen Rubell and attorney Ian Schrager have a successful disco called Enchanted Gardens which was once the Douglaston (L.I.) golf course. The third partner is Jack Dushay, who would identify himself only as having had retail stores and formerly being in real estate in the Washington area.

"It's like theater. We want things to happen all the time," Dushay shouted over the rock music and certainly for the opening nothings stood still.

For starters there was the Firoucci fashion show of T-shirts, sweat shirts with airbrushed subway graffiti, designed by illustrator Antonio Lopez and dancing by members of the Alvin

For the second number the dancers wore capes lined in colored metallics, the boys in pants with a metallic stripe, the girls in fringed skirts and gold fabric corselets which Fiorucci will carry shortly.

As at the popular year-old Fiorucci on East 59th Street, a lively open-street market setting where a lot more happens than the clotes, a lot was going on at Studio 54.

The big action was on the dance floor where, in the anonymity of the huge crowded area, men as well as mixed couples danced together. The mood was changed dramastically from dark to sunlight by adjusting the lights left behind by the television studio, plus many more, and by constantly changing mylar strip curtains and huge backdrops - all planned, designed and choreographed by theatrical lighting designers Jules Fisher and Paul Marantz, the lighting team for the Rolling Stones, American Buffalo, the Oscar awards and other projects.

The $64,000-question for Studio 54 is whether the crowds will keep coming back. Unlike some discos where loyalty falls off when popularity takes over, Studio 54 will need popularity to look crowded.

"For a lot of blue-collar working kids - hairdressers, store clerks, even low-echelon professionals - dressing up to go dancing and be seen is where they spend most of their money," said Owen Levy, a publicist and observer of the disco scene.

"When people come here, they can play out their fantasies with others watching with binoculars from a balcony. How can you resist? For one night it makes you feel you're really making the scene and that's what's really most important."