The three stories in Offenbach's "The Tales of Hoffmann" are notoriously hard to pull together, but in the new "Tales" that opened the Metropolitan Opera's season here last night the Met has found the formula.

The most publicized star of this production was tenor Placido Domingo in the title role, though he could not make it for the tour. But the real stars are not singers; they are Otto Schenck, the director, and Gu nther Schneider-Siemssen, who designed the wonderful sets.

Whatever the Met paid for all this, and it looks like they paid a lot, the company got its money's worth. The production seems sometimes truer to the spirit of E.T.A. Hoffmann, and his fixation with the delirium of love, than the opera itself. It is somber enough to allow for the grotesque side of Hoffmann's tales and bright enough to express the euphoric romance. This is not just a splashy display they have created, it is compelling drama.

The other ingredient in the formula is strong casting of the 14 principals, and in that respect the Met failed to follow its own formula in some key roles. Seven of last night's singers were substitutes for the singers who sang in the debut of this "Tales" less than two months ago, and with one or two exceptions the new singers diluted the performance.

One of the three soprano leads, coloratura Ruth Welting, who also starred in the original, was brilliant as Olympia, the mechanical doll with whom Hoffmann fell in love in the first tale. Her characterization was a rare blend of musical and dramatic casting. The dazzling little voice is right for the role's high pyrotechnics and her tiny, doll-like bearing could have been tailor-made for the part. Welting's acting as the little doll that moves in jerks and occasionally starts to sag as she needs winding again was remarkable.

Neither of the female leads in the other two tales offers quite such an opportunity. But substitute Rosario Andrade, as the dying singer Antonia in the last tale, made a strong impression. She conveyed the character's vulnerability with warmth. And in working with conductor Julius Rudel, also a substitute, she brought things together with a force and control that had earlier eluded him.

Stepping into Domingo's shoes in the title role was a thankless assignment, and last night's tenor, Kenneth Riegel, is no Domingo. It would be nice to report that he compensated for his weaker sound and lack of clarion-like resonance with elegance of phrase and dramatic intensity, but that was not the case. In the prologue, the orchestra often blanketed him, including one spot where it took no more than a solo horn. The part demands a bigger voice.

There was nothing small, however, about the voice of bass James Morris, who sang the villains in the three tales, and the mean Lindorf in the prologue and epilogue. His aria, "Scintille, diamant," in the Venetian tale was positively Mephistophelean, as were his melodramatic costumes and makeup in all the tales.

Ariel Bybee was splendid in the dual roles of Hoffmann's sidekick and as the Muse of Poetry.

But the other leading female, Isola Jones, as the Venetian courtesan, sang indifferently and broke the mood during her curtain calls by playing cutsey with the audience and then gesturing her colleagues back for more bows with a bent finger.

If the Met orchestra was not quite up to its considerable best, the chorus most certainly was. Its drinking song positively swaggered.