After five years of planning, composing and rehearsing -- and delays, frustrations and postponements -- Krzysztof Penderecki's long-awaited opera "Paradise Lost," one of the largest musical efforts of the last half-century, finally had its world premiere Wednesday night.

The audience, many of whom expected to hear music of dissonant, grating sounds, interspersed with violent screams from the chorus, was surprised to hear music of vivid imagination, but music that did not violate their ideas of great choral and orchestral textures.

The sets, costumes and stage props alone for this vast production cost about $450,000, and the final bill is expected to be in excess of $1 million. The opera was originally commissioned from the influential Polish composer in 1973, for the 1976 Bicentennial, but delay after delay heightened the sense of drama present Wednesday at the 3,500-seat Civic Opera House, where the Lyric Opera production had long since been sold out.

The work, based on Milton's epic poem and with a libretto by British playwright Christopher Fry, was designed in partnership with La Scala in Milan, where the opera will have its European premiere on Jan. 23 under the composer's baton.

The music marks a turning point in Penderecki's basic style, though one he anticipated in a violin concerto he wrote several years ago. It is highly tonal, with a long sustained opening over a low B flat, and ending in a blazing chord in E Fiat very much like "Ein Heldenleben" by Richard Strauss.

"This is not music by the angry young man I used to be," Penderecki said at a press seminar on Tuesday in Chicago where nearly 100 music critics had gathered to listen to the composer and scholars discuss the music and Milton's poem.

In a sense, the new opera closely observes familiar operatic conventions: There are extended solo scenes, duets, trios, and larger ensembles.

In another sense, it departs from, or expands those conventions. The enlarged chorus of 100, which carries a large part of the sung portion of the opera, is stationed throughout in twin transparent towers placed at either side of the stage.

The towers caused last-minute revisions in the staging of the opera. Built it Italy, they were declared on arrival to be insufficiently sturdy to hold the singers while being moved about the stage, a dramatic effect Penderecki greatly desired. By the time they were rebuilt and reinforced, the towers were no longer movable.

The chorus, magnificently trained by Rogert Page, made a profound impression throughout the three-hour score, in which they are called upon to hum, to hiss, to shout, and to speak, all in addition to singing of a beautiful but extremely demanding kind.

The towers were not the only staging problem: Stage director Virginio Puecher resigned a week ago Monday, just nine days before the premiere, after what general manager Carol Fox called "areas of disagreement between him and the composer."

Penderecki simply said, "As rehearsals progressed, I found that my own vision of the opera I have created was in conflict with Mr. Puecher's directorial concepts." Fox added, at Tuesday's seminar, "In any such difference, the composer always is the final authority."

The staging was then taken over by Igal Perry, who earlier had been engaged to assist choreographer John Butler with the vital element of dance, which dominates much of the opera.

It is, indeed, the dance that sets this opera apart from all others. For while there have been a few operas in which major areas of the action have been carried on in choreography -- Rimsky-Korsakov's "Golden Cockerel" among them -- those operas were not originally planned with dance in that manner.

From the beginning, Penderecki, whose dramatic instincts seem as outstanding as his musical gifts, conceived of the roles of Adam and Eve as sung and danced -- by a baritone and soprano, and by principal solo dancers. As it turned out, nothing in Wednesday night's premiere was more impressive, or at times more deeply moving, than the erotic innocence of that first man and first woman dancing, in Butler's superb fluent poetic movements, in the power of their new lives.

The murder of Abel by Cain also was powerfully managed -- entirely in dance.

To many eyes in the opera house, the dancers looked, as Milton wrote, "in naked beauty more adorn'd, move lovely, than Pandora." Actually, Nancy Thuesen's Eve was clad in the sheerest body stocking, and Dennis Wayne wore a similar cover where centuries of tradition have put the fig leaf. After the pair tasted the fruit of the tree of knowledge, their altered condition was symbolize by having the singers change from white robes to deep red.

The extended use of chorus and dance was only a part of Penderecki's immense concept. From the first notes, taking the fullest advantage of a Wagnersized orchestra of 96 pieces, plus organ and added sound effects, he created a panorama of sound against which the immortal conflict between Satan and God could be played out.

To musicians the composer signals this conflict with the very first chord in his score: Over the low B Flat, he places an E natural, creating the long-forbidden interval call "Diabolus in musica -- the devil in music, the tritone." Later on, his orchestra creates the threatening rattles of the approaching serpent as Satan persuades Eve to taste of the fruit of good and evil; it roars in despair in the awful visions that follow Adam's and Eve's fall, as visions of Cain murdering Abel, of pestilences, the Flood, and of wars sweep across the stage. It is reported that Penderecki's score has "VIET NAM" written across the passage in which the victims of war are seen and heard.

But Penderecki also has created vocal passages of great beauty: A duet for Adam and Eve rises to ecstatic heights to end on a note of perfect peace, a duet that would, in most opera houses, under more ordinary circumstances, bring on a prolonged burst of applause. That it did not on Wednesday seemed probably the result of a kind of intense concentration and awe in the face of some epic music on a limitless subject.

There are lovely solo pages for Adam and for Eve, a charming children's chorus when the animals are brought in for Adam to name: the camel, the lion, the tiger and the elephant, the giraffe, and the swan.

The last of these creatures brings out the first of three direct quotations Penderecki uses during the opera: When the swan appears, the orchestra plays the opening measures of "Lohengrin." Later on, at the beginning of one of the most menacing visions, the chorus intones the "Dies Irae;" and when the Messiah appears, asking God, "Father, behold me, then. Me for him, life for life, I offer," Penderecki overwhelms his listeners by having the chorus sing a verse of the chorale "O Wondrous Love" from the St. John Passion by Bach.

Other parallels are more in the nature of conscious or subconscious echoes: a chord that sounds right out of Strauss, another like Mahler; one, even, straight out of Ravel. In other words, the orchestral fabric is of incredible richness.

After a single hearing, some questions remain that repetitions will answer: Is the opera as static as if often seemed, with some of Satan's longer soliloquies sounding like a tired Wotan? Are the two acts, each one lasting an hour and a half, longer than the unchanging slow action can sustain?

It is important to note than Penderecki calls "Paradise Lost" not an opera, but a "sacred representation." (Mozart calls "Don Giovanni" a "dramma giocosa " (humorous drama), and Strauss-Hofmannsthal labeled "Rosenkavalier" a "comedy with music," so the label does not matter.) But there is more than a hint that "Paradise Lost," with its huge production costs, may have a longer and stronger future in concert form, perhaps with movement and dance, but without the great vaults of heaven and hell.

The Chicago production, which will go "lock, stock, and barrel," to La Scala next month, is extremely handsome. Designed by Ezio Frigerio, it is lighted, not always satisfactorily, by Gil Wechsler. Too often, near-darkness onstage prevented any clear realization of what was happening, especially in the hellish visions.

Conductor Bruno Bartoletti, in the composer's words, "came closer than anyone else I have known to the meaning of my music." The singing was always better than adequate, and from William Stone as Adam and Ellen Shade as Eve, of extreme beauty. Joy Davidson made Sin a thing to admire, while Paul Esswood's countertenor almost made Death seem welcome.

The cast is too large to name in full, but it was excellent, not least of all for the clarity of its enunciation.

Future productions will reveal new facets of the work. It is too soon to know how and where it will make its place. On Wednesday night there were times when a change of mood, a furious presto, or even a judicious cut-seemed advisable. Penderecki plans no changes, other than a slight extension of one of Satan's scenes, and the addition of a brief interlude.

On Wednesday, the audience, which had listened attentively, applauded warmly, but without the kind of rapture that marks the instant success. And the applause ended in about five minutes, which, after so substantial a work, is modest indeed. A final verdict is by no means yet possible.