Published: October 18, 1983

With any luck, the Metropolitan Opera's Centennial Gala this Saturday will behave like one of those big people on the dance floor who amaze everyone for their lightness of foot. The celebration will be huge - with big arias, duets, trios, big audiences, big stars, big egos - all of which are going to have to maneuver delicately within one opera house and a finite amount of time.

There will be Placido Domingo in the afternoon and Luciano Pavarotti in the evening. Birgit Nilsson will sing Wagner, Joan Sutherland Rossini; and interspersed will be, by last count, 94 other singers, some with sizable names, some with smaller ones, but all equally determined to share in the festivities.

It is a two-part event - four hours in the afternoon, four in the evening. At least, that is the way it is planned. Within this framework, 48 numbers led by six different conductors are going to have to fit in. The Met's ballet will also be there. And the Met's orchestra will play and play and play. Public television is sending it all live to the United States and Europe - all of it.

The Met Gala is supposed to be a celebration of opera's graces, and the house's backstage planners have spent most of the last two years trying to keep it from lumbering into an uncontrollable, elephantine marathon. They think they have it all figured out. Entrances and exits have been timed and re-timed, pauses between numbers calculated and a certain flexibility mixed in as well. There will be five different sets from five different Met productions but only the ballet dancers, in the bacchanal from ''Samson et Dalila,'' will be costumed. Cooperation and Enthusiasm

Met officials say that cooperation and enthusiasm among all concerned have been exemplary, but it is hard to imagine total sweetness and light among the opera world's eminently bruisable egos. Charles Riecker, the artistic administrator at the Met and the man responsible for assembling this small army of operatic stardom, speaks proudly of how, for example, Regine Crespin and Marilyn Horne will fly in from California between other scheduled performances, how Katia Ricciarelli will arrive only on the morning of the performance, how Miss Nilsson and Eva Marton are coming all the way from Europe. Artists are being paid a uniform honorarium and travel expenses, he said.

But how, for example, will the Met solve the sensitive problem of who gets what dressing room? ''There won't be any dressing rooms, or at least all of them will be open to everyone,'' said Joseph Clark, the Met's technical director. ''Singers will come to the Met dressed in advance. We'll have makeup people to help adjust for the television cameras, and there will be a color monitor backstage so everybody can see what they will look like on the screen.'' How many phone calls did it take to assemble this cast? Probably a thousand, Mr. Riecker said.

Is the Met Gala going to be too much? Is an operatic orgy imminent, and are we going to need a cultural Alka-Seltzer when it's all over? And would a slimmer, more graceful commemoration have been more appropriate? Mr. Riecker thinks not: ''My experience is that real fans can never get too much opera.''

The Met's first performance - on Oct. 22, 1883 - was Gounod's ''Faust,'' but the house has decided that a revival of an opera long out of the Met's repertory was not the right form of celebration. ''Yes, we thought of 'Faust,' '' said the Met's general manager, Anthony Bliss, ''but there are so many singers who want to take part that we could not really do justice to the company with one opera featuring only four or five principals. We also decided that this event should represent a thrust into the future more than a look into the past.'' A Great Deal of Subtlety

James Levine, the Met's music director and the principal builder of this long afternoon and evening program, has handled the problem of assigning repertory with what seems to be a great deal of subtlety. He may have avoided squabbles over prominence and precedence by placing most of the biggest names in duets - Mr. Domingo with Mirella Freni, Mr. Pavarotti and Leontyne Price, Sherrill Milnes with Ruggero Raimondi, Jessye Norman and Jess Thomas, Jose Carreras and Montserrat Caballe. Could this be a wise way of avoiding jealousies through an appeal to the singers' sense of noblesse oblige?

Kiri Te Kanawa will appear alone, however, as will Joan Sutherland, and other arias are allotted to James McCracken, Miss Crespin, Miss Marton, Nicolai Gedda and Ileana Cotrubas. Miss Nilsson will sing from ''Tristan und Isolde'' and Miss Horne from ''Samson et Dalila.''

Mr. Levine is scheduled to do the most conducting, but Leonard Bernstein will open the evening's performance with the Leonore Overture No. 3 by Beethoven. Jeffrey Tate will also conduct, along with Richard Bonynge, Sir John Pritchard and David Stivender.

The Met roster for this two-part gala is impressive for those who are on it and intriguing sometimes for those who are not. A Couple of Puzzlers

Carlo Bergonzi, the elegant tenor who has sung so wonderfully at the Met, will not be coming from Europe, though he was invited. But more puzzling is the absence of Jon Vickers, the great Canadian tenor who is in New York for performances of ''Peter Grimes'' at the Met, but who has declined, Mr. Riecker said, ''for personal reasons.'' Erich Leinsdorf, a conductor at the Met since 1937, is appearing in Washington and will not be present. Mr. Riecker said that Pilar Lorengar and Leonie Rysanek wanted to come but were obligated elsewhere.

A heartening inclusion, on the other hand, is Mr. McCracken, the American tenor who has feuded with the Met in recent years but is returning to the house next season for the first time in five years.

Aside from the human problems, there will be the purely physical ones - for example, the juxtaposition of five different sets no one of which was designed to be used sequentially with any other. The intermissions for this telecast range from 25 to 30 minutes, so timing is everything.

The clock is also crucial for assembling performers offstage and getting them gracefully on and off. ''What we've tried to compensate for in advance,'' said Michael Bronson, the Met's media department director and executive producer for the broadcast, ''is the unexpected. When we've televised operas at the Met in the past, our directors have gone to rehearsals, considered their choices and planned ahead. For the gala, we're having rehearsals Thursday and Friday, but there's no way all the singers can be there in sequence. 'Out of Our Hands'

''Out of three and a half hours for one segment of the gala, only about 50 to 75 minutes of that ends up being music,'' Mr. Bronson said. ''Moving people and material is the rest. A lot of that we can control. But when Birgit Nilsson comes out on stage, and the audience wants to applaud for several minutes, that's out of our hands.'' Phebe Berkowitz, the Met's executive stage director, anticipates another possible and opposite problem - how to deal with last-minute cancellations and their effect on timing. Intermission features will include historical films and, said the Met, ''a few surprises.''

The gala, which will be shown on public television from 2 to 6 P.M. and then from 8 P.M. to midnight, is part of the Met's continuing campaign to win support from the country as a whole. ''Eighty percent of the 50 major public television outlets to whom we offered the gala are taking both parts live,'' Mr. Bronson said, adding ''Texaco is providing a lot of the money toward financing the gala.''

WQXR will broadcast a simulcast of the gala on AM and FM, as will some public radio stations around the country.

The Met's planners will be working and rethinking this giant enterprise until the last minute, but luck will still be involved. ''The afternoon program ends at 6 P.M.,'' Mr. Bronson said, ''but we have planned flexibility and we don't expect to have any singers left over. If it does happen, at 6:01 you're going to see me running out into traffic on Amsterdam Avenue.''

Mr. Bronson, who is a very, very busy man these days, said he is having fun but added, ''Fortunately, you only live to be 100 once.''