An unwelcome duplication if there ever was one, "Superman III" sticks to the jaundiced, self-defeating pattern that left "Superman II" in such wretchedly disillusioning shape. In fact, the most appropriate title for the new film would probably be "Superman, Psycho."

Early indications of humorous zest and likability--recruiting Richard Pryor in a principal comic role and arranging a new romance between Christopher Reeve as Clark Kent and Annette O'Toole as former high school heartthrob Lana Lang--are eventually betrayed by massive applications of tacky workmanship and cynical degeneracy.

Like its immediate predecessor, "Superman III" continues the strangely miscalculated, mean-spirited dismantling of the heroic myth that was rejuvenated in a spectacularly amusing, ingratiating fashion by newcomer Reeve and director Richard Donner in "Superman." The lingering mood of ill will left by the first sequel can only be enhanced by "Superman III," opening today at area theaters.

Its efforts to rationalize a situation in which the hero becomes his own worst enemy and must subdue an evil alter ego in hand-to-hand combat certainly leave the exposition in a humorless schizoid fix. The principal novelty of Reeve's once irresistible impersonation of Superman and his placid human front, Clark Kent, is the emergence of a temporary, utterly gratuitous malicious personality, which causes the hero to act despicably for a tedious stretch.

Of course, it's always been a problem inventing plausible threats to the Man of Steel, who is nearly invincible by definition. There's the Achilles' heel of his vulnerability to Kryptonite, the antagonism of incorrigible criminal masterminds like Lex Luthor, the appearance of other survivors from the extinct planet Krypton, or sudden mental disorder and personality splitting. Director Richard Lester and the screenwriting team of David and Leslie Newman exploit all these dodges in a disagreeable way, betraying an apparent craving to see the Superman character systematically, grotesquely degraded.

In "Superman III" the hero himself becomes an economical substitute for the trio of creepy seditionists from Krypton who terrorized the Earth in "Superman II." This internal, fake-psychological threat is poorly stitched to an external threat feebly contrived around a set of comic villains similar to the trio embodied with underrated skill and amiability by Gene Hackman, Ned Beatty and Valerie Perrine in the original film. The new group features Robert Vaughn, Pryor and Pamela Stephenson in the more or less equivalent roles and throws in a mirthless, superfluous addition in Annie Ross as the mannish sister of Vaughn's character, a power-hungry corporate tycoon called Ross Webster.

Coveting financial control of any commodity or market that takes his fancy, Webster exploits the ill-defined technological genius of Pryor's character, Gus Gorman, a nervous nonentity who discovers a mysteriously magical touch with computers once he begins working behind a terminal at Webster Inc. In fact, Webster has Gorman over a barrel, since the new employe has demonstrated his dexterous initiative by directing the payroll computer to write him an extra check that amounts to five bulging figures. A scheme to corner the coffee market by inflicting a tornado on Colombia is foiled by Superman, driving Webster to retaliatory schemes that pit the hero first against his vicious punk of an alter ego and then against a despotic master computer (uh-huh, one of those again) constructed in a cavernous hideaway in the Grand Canyon.

Why should Superman, of all conceivable good guys, harbor a vicious punk of an alter ego? What's supposed to happen is that Gus supervises the manufacture of a synthetic hunk of Kryptonite and then delivers it to Superman, who suffers delayed-action effects that bring out a submerged rotter.

Unfortunately, the role of Gus is a fundamentally duncey wad of mannerisms, at best baggily tailored to Pryor's talents, and the unfunniest single "highlight" of the role emerges when Gus is meant to slip Superman that Kryptonite mickey. The situation obliges Pryor to do a George-C.-Scott-as-Gen.-Patton impression that falls so agonizingly flat you're cringing too much to pay sufficient attention to the Kryptonite angle, which seems harmless anyway after Superman shows no immediate ill effects.

Ultimately, Reeve as Clark must overpower Reeve as the demented Superman in a wrecking yard. When Clark is hurled into a huge compactor and apparently squeezed into so much squared-off metallic junk, "Superman III" reaches its logical consummation. It's sheer anticlimax to go through the motions of reversing directions in a heroically satisfying way. The filmakers pretend to brush off the ponderous spectacle of self-abuse they've actually wallowed in. Clark prevails, Superman is supposedly made whole again and goes on to face the belated threat of the despotic computer, but the bad vibes have ground one's tolerance into dust.

Every composite shot in "Superman III" appears to be a careless affront to the willing suspension of disbelief. The flying sequences are a letdown, the cataclysms are a cheat, and even the settings are often exposed as a chintzy hoot--especially when Reeve momentarily grips a rock in one of the Grand Canyon sequences and the Styrofoam gives spongily right before your astonished eyes.

There's one choice sight gag--Pryor apparently skiing down the side of a glass skyscraper--and if you had to leave the movie after perhaps the first 40 minutes, you could cherish the delusion of having missed a good time. Margot Kidder makes a token appearance as Lois Lane, but the romantic interest is meant to shift to O'Toole, and this switch might have been delightful if the filmmakers had followed through on its most amusing hint--Lana Lang, now a struggling single mother, is more attracted to steady, down-to-earth Clark than to glamorous, glorious Superman.

Reeve, the ongoing justification for the series, is no longer contractually obligated after this episode, and his liberation comes not an installment too soon.

After the screening an equally disaffected friend asked, "What's next? Dressing Superman up in a skirt and having him act out a sexual identity crisis?" Not quite. But "Supergirl" is in production. SUPERMAN III

Directed by Richard Lester; screenplay by David and Leslie Newman; music by Ken Thorne; original songs by Giorgio Moroder; edited by John Victor Smith; director of photography, Robert Paynter; produced by Pierre Spengler; executive producer, Ilya Salkind. Released by Warner Bros. Rated PG. THE CAST Superman Clark Kent....Christopher Reeve Gus Gorman....Richard Pryor Perry White....Jackie Cooper Jimmy Olsen....Marc McClure Lana Lang....Annette O'Toole Lorelei Ambrosia....Pamela Stephenson Ross Webster....Robert Vaughn Lois Lane....Margot Kidder