LEAD: The Alden twins, David and Christopher, are honorable, sometimes outrageous variants of Peter Sellars - directing contemporized versions of standard operas, which some people love and some people despise.

The Alden twins, David and Christopher, are honorable, sometimes outrageous variants of Peter Sellars - directing contemporized versions of standard operas, which some people love and some people despise.

But one thing Christopher Alden has at the Opera at the Academy in New York City that he lacks at the Long Beach Opera in southern California is an audience that mirrors his sensibility. On stage, he puts a jeunesse doree of wealthy social butterflies and fashion-conscious hangers-on, full of miniskirts and mink and decolletages. And at Saturday night's opening of his new production of Offenbach's ''Vie Parisienne,'' he had exactly the same thing in his gala audience. (Come to think of it, he may have gotten a comparable crowd when this same production was offered in October in West Hollywood.) All of which made for about the most successful Alden production this writer has seen. Part of its success was due to the sheer cleverness of the staging, the skill of its execution and the ingenuity of Christopher Berg's musical arrangement, not to speak of the enduring charm of the work itself. Part was due to the fact that Offenbach, not usually a creator of sacrosanct masterpieces and full of a lively sense of social satire himself, is perhaps more suitable to free contemporization than, say, Mozart or Wagner.

But an equally large part was the parallels between the Second Empire Parisian demimonde celebrated and lampooned in ''La Vie Parisienne'' and its precise equivalent in New York today, as underscored by Mr. Alden. Opera at the Academy performs in a tiny rectangle surrounded on three sides by its audience (capacity is 120). When characters entered through the seats dressed exactly like Saturday opening-night gala partygoers, the spectacle spilled fascinatingly - even a bit scarily -from performers to observers and back again.

Given the fact that this production offers drag acts, garter belts, whips, seminudity and about eight million double-entendres, it's surprising how little has actually been changed from Offenbach's 1866 original and from the frothy, clever libretto of Henry Meilhac and Ludovic Halevy. The uncredited English translation updates things wittily without undue anachronism. The occasional number has been cut or altered, but the revisions aren't too radical. Mr. Berg's reduction for chamber ensemble is imaginative and ebulliently performed.

About the only regret is a rather too leaden attempt to invest the proceedings with anarcho-Marxist underpinnings. Marxist slogans surround the playing area, and the character of Frick, the German bootmaker, has been inflated into that of a plotting anarchist who blows everybody up at the end. The protofeminist pride of the courtesan, Metella, has been given a curdling element of late-1980's rage, and the duped baron's disappointment at the end escalates from an almost-duel to a near-murder. Yet the atmosphere remains mostly light and truly amusing, and the Second Empire flavor has hardly been eradicated.

As with any good production, good people have been cast and cleverly directed. Nearly everyone here can act, some of them very well indeed -above all Henry Stram as the anarchist; Mark Janicello as Raoul, the leading man; Felicity La Fortune as Metella, his punk girlfriend; Daryl Henriksen as the duped Swedish baron, and Angelina Reaux as Gabrielle, a glove-seller.

They can sing, too: Miss La Fortune, despite a curious register break, revealed a pretty little vibrato, and Miss Reaux, fresh from Mimi for Leonard Bernstein and a Kurt Weill one-woman show at the Public Theater, delivered Gabrielle's numbers with considerable oomph.

Mr. Janicello has a nice tenor, and there was serviceable baritone singing from Mr. Henriksen and Michael John Lindsay as Bobinet, friend of Raoul. Badiene Magaziner-Gray did a good job as the baroness, and the lesser roles were neatly handled, too - although everyone suffered from the inevitable problem of blasting stentorian operatic singing and acting five feet from the audience's ears.