Having had not a single good review - nor a single empty seat - in Chicago, San Francisco and Los Angeles, Liza Minnelli arrived in "The Act" Saturday night at the Majestic Theater for the most clangorous opening of the year.

Crowds blocked 44th Street, cops rerouted traffic and gawking at glittery ticket-holders delayed the 8:30 curtain 20 minutes. Nobody minded. People almost toppled off balcony and boxes to stare at Elizabeth Taylor, Sammy Davis Jr., Ethel Mermen and Martha Graham down front, a quartet rarely glimpsed in a single glance.

Originally known as "In Person," its book by George Furth and score by Marvin Hamlisch, the play had gone through the customary hemming and hawing of producers and actors. Who would risk how much on what stars? Rising costs delayed decisions. Such actresses as Shirley MacLaine, Ann-Margret, Mary Tyler Moore, Debbie Reynolds and Doris Day were mentioned.

Enormously popular with a cult, Minnelli has been big in the clubs but no great draw as a movie star. But with her night club turns by John Kander and Fred Ebb, who wrote "Cabaret," her sole socko film, Minnelli had material everyone envied. With them as composer and lyricist to replace the Hamlisch score, she opened the work in Chicago on July 4 as "Shine It On," now the show's opening number.

Changes, rumors, and advice from "play doctors" filled the gossip columns. ("You ever have trouble with a show? Double that and you're not even close to what we've been through," said one person involved with it from the start.)

Martin Scorsese ("New York, New York") was the original, Minnelli-appointed director, though stage work was new to him. His name remains on the program. But the informally admitted director for the past four weeks has been Gower Champion. (At a cast party in Central Park's Tavern on the Green in the wee hours of yesterday, hero Champion, now beardless, was nowhere to be seen. And when Minnelli entered her own party, it was with producer-husband Jack Haley Jr., whose father had been with Liza's mother in "The Wizard of Oz." At the end of Minnelli's covey of eight trailed a minute Scorsese.)

Among other pre-New York problems, flashbacks in the plot had confused some audiences and the critical reports had been scathing. A miracle was needed and it seems to have happened.

"The Act" is Liza Minnelli. Rarely has a vehicle been so tailr-made for a star. Well over a million dollars has gone into. "The Act," the price scale is the highest ever - from $9.50 up top back on Wednesday matinees to $25 down fron on Saturday nights - and the big Majestic will be able to gross a whopping $238,135 weekly.

"The Act" is a swell show which does exactly what it sets out to do, show off the striking, vital talents of Liza, unveil some grand songs from Kander and Ebb and reveal, through seven immensely individual dancers, some dazzling choreography by Ron Lewis, a Las Vegas favorite in his musical theater bow. I could see "The Act" again just for this small but dashing chorus line.

The setting is a Las Vegas hotel where a second-rate movie star is making her night club bow. After mistaking her missing shoe for a microphone. Michelle Craig goes into her specialty numbers while remembering career and marital incidents which led to her present uncertain status. Her older director-husband, a footless lover and a gay composer flow in and out of her past and present. By the end of her act, Mike Craig will have her audience and life in control.

The story by Furth, who wrote "Company" and "Twigs," is hardly new but the trappings are. Using the act for the action allows for a grand variety of Kander-Ebb songs. "Turning," with the dancers whirling on poles; "Arthur in the Afternoon," a comic song about extra-marital sex; "City Lights," not unlike "Annie's" "Easy Street" swing; "Hollywood, California" ("He was the stunt man in 'Deep Throat'"): "Hot Enough for You" and "There When I Need Him," a Garland-type ballad, lead up to a self-examining finale. "My Own Space."

In all these numbers, the Lewis dancers, four men and three girls, accomplish some rousing turns, all but one of them with Minnelli at the center. Her Halston clothes, as often as not pants, have glittering, spangled simplicity, ranging from white through purplish blue, various reds, greenish blue, gold, black and green. It's a great parade and she's got great legs, a permissable observation. I trust, when dealing with female dancers.

Ebb's lyrics shine: "Country air means zilch to me. I won't breath what I can't see" going over especially well with New Yorkers who proudly applauded references to the city's squalor. "City Lights" seems to begin as a paean to country joys but becomes a hymn to the Manhattan skyline.

With Stanley Lebowsky's 26-piece orchestra on both sides at stage rear and a revolve which rises and falls, the Tony Walton scenic designs open up like a camera's eye. Tharon Musser's lighting is her splashing, colorful best.

Through all this Minnelli ambles, struts, parades, hoofs, hunches, stalks, tippy-toes, prances and stands stock still, every move perfectly coordinated. Her voice booms or caresses, catches or throbs. Her face is irregular, long nose and face topped by that dark bob which curis down her cheeks. Her watchable quotient must bat a thousand. Half the numbers prove show-stoppers.

As the preoccupied but lovin' husband, Barry Nelson is a restrained body of strength, at one point popping up from the audience, always sure with his points, a solid leading-man co-star. Arnold Soboloff is amusing as the composer and Roger Minami, as "Arthur in the Afternoon," is brilliantly funny as he twirls his suspenders to indicate pleasure.

What will happen to "The Act" once Minnelli leaves, the end of July at the latest? The general concensus of first-nighters was that "The Act" would have to end. I wouldn't be too sure. Once a show gets going, as this is most likely to do, the irreplacable seems replacable. Minnelli followed Gwen Verdon in "Chicago," Robert Preston took over "sly Fox" from George C. Scott and another star wants in after Preston leaves. It's a new trend. Would Streisand risk it? What about her unknown sister? Or Minnelli's sister? Or a total unknown? Or an older star?

That the Kander-Ebb songs and Lewis dancers would just disappear seems unlikely. The songs will be recorded next Sunday and the record's bound to sell big.

And speaking of records, the word is that there also may be a recording of the Hamlisch-Furth to original.

When Champion - who has performed such past miracles as the original "Hello, Dolly!," "Irene" and the current Debbie Reynolds revival of "Annie Get Your Gun" - was brought in, he set out to give form and pace to the story and staging. He pretty much succeeded.

For the overriding feel of "The Act" is its professionalism, from performances to details. Within four months the first three cities have paid off half the initial investment and though further money has been spent liberally, a New York smash could redeem the budget.

Relaxing in the early Sunday hours for their first day off since June, Minnelli and the cast had a ringing party at the Tavern in Central Park.

Paying court to Martha Graham at the party were such other choreographers as Michael Bennett of "A Chorus Line," Bob Fosse of "Cabaret" and Ron Lewis of "The Act."

Such producers as Robert Whitehead and Alexander Cohen, not in on this action produced by Feuer and Martin and The Shubert Organization, voiced trepidation about Minnelli's distant departure. When composer Jule Styne, whose "Funny Girl" put Streisand on the map, was asked whether maybe Barbra would risk the part, he said: "That lady's not crazy. She could do one of these on her own."

"The Act" will be a legendary musical. How often does the striking daughter of a striking mother star on the Broadway musical stage? Little Liza's powerhouse.