"Rocky III" is an engaging exercise in discreet, incisive and good-humored hokum. Sylvester Stallone looks almost surrealistically fit, his features so impressively chiseled above the neck and muscled below it that he puts his own statue to shame during an unveiling sequence outside the Philadelphia Art Museum. He's become statuesque to an astounding degree. Yet, although "Rocky III" is a vivid piece of popular filmmaking and a considerable bit of harmless fun, the star doesn't seem to derive as much pleasure from the experience as he should.

The hang-up, I suppose, is Stallone's justifiable fear that Rocky is the only role that may work for him. This doubt seems to be lurking behind the material in the script that emphasizes Rocky's doubts about a comeback effort. Presumably, it's the impulse behind a speech like "You wake up after a few years thinking you're a winner, but you're not, you're a loser; I don't believe in myself anymore; I don't wanna lose what I got."

Echoing the bad judgment of Tom Laughlin in "The Trial of Billy Jack," Stallone permitted the lucky charm of "Rocky," the Cinderella hit of 1976, to tempt him into a vanity sequel of stupefying mawkishness.

In "Rocky II," again directing from his own screenplay, Stallone allowed himself the near-blasphemous luxury of scenes in which Rocky carries on one-sided conversations with an invisible Best Pal and Number One Fan, God Almighty. In "Rocky III" the hero's piety is much improved by being limited to the act of crossing himself in his corner before each bout.

When Mrs. Rocky, the erstwhile wallflower Adrian, was felled by a mysterious coma in mid-pregnancy in the original sequel, Talia Shire was obliged to lie still while Stallone blubbered over her prostrate form for a reel or so, making a bathetic spectacle of himself. The equivalent episode in "Rocky III" is much more sporting: Stallone and Burgess Meredith, reviving his overfamiliar role as the irascible trainer Mickey, perform a kind of dueling whispers duet when Mickey's ticker fails him before a title match and Rocky comforts his fallen mentor.

Stallone even tries to make it up to Shire for his inability to think of things for Adrian to say all these years. Now she gets to deliver the stern, morale-restoring, pull-yourself-together-man, you've-never-been-a-quitter speech that stiffens Rocky's spine and opens his eyes just as he's tempted to throw in the towel and retire.

"Rocky II" tried to sustain a repetitive plot on overdoses of masochism and hostility. Stallone depicted Rocky descending from fame to squalor soon after his gallant match against the cocky heavyweight champion Apollo Creed. Desperate to get the characters back in the ring for a cinematic slugfest, Stallone violated the traits that had made them appealing and pretended that Rocky was an incorrigible bum and Apollo a mean-spirited, vindictive champ. The rematch exchanged bruising mutual gallantry for vicious mutual bloodlust.

Stallone attempts to repair some of the damage in "Rocky III." Instead of returning to the garbage heap, the narrowly victorious Rocky is shown retaining his title through an opening, updating montage of 10 (!) title defenses. All in all, the Rocky Balboa Family seems content with the status and prosperity that flow from athletic celebrity, and Rocky proves an exemplary champ. There's an exaggerated display of drunken resentment from Burt Young as Adrian's slobby brother Paulie in the early going, but Rocky pacifies him so promptly that his potential troublemaking is instantly transformed.

A sneaky sense of humor has always been one of Stallone's assets, and it's keenly evident in the depiction of Rocky's reign. For example, it's typical of Stallone to imagine Rocky doing ads for American Express (could the public have forgotten him already?) and the DeLorean luxury car and to work in amusing inserts like his own appearance on "The Muppet Show." The scene for a wacky early episode, in which Rocky faces a berserk heavyweight wrestler named Thunderlips in an exhibition match, is set by this characteristic exchange between Paulie and Rocky: "Nobody does this much for charity." "Bob Hope does."

A miserable pretext in "Rocky II," the animosity between Apollo and Rocky is purged from "Rocky III," which shows Apollo, again played by Carl Weathers, encouraging Rocky's comeback and supervising his training after Rocky loses the title to a seething brute called Clubber Lang. So a professional alliance is formed between Apollo and Rocky in order to restore the heavyweight crown to a noble pugilistic type.

Rocky is obliged to do it One More Time, but the clever commercial switch is that he couldn't do it without entrusting his training to Apollo, who forces him to abandon his flatfooted slugger's style and come at Clubber like the young Muhammad Ali--dazzling his scowling opponent with fleet footwork and lightning combinations.

For some reason, Rocky waits to unveil his classy, devastating new style until Clubber has tired himself by landing several dozen numbing haymakers, but all common-sense objections are mere quibbles at this stage of the fantasy. Rocky's Ali-style comeback as a great black boxer is obviously farfetched. The indispensable comic resource in the whole fabrication is the performance of the former jock and professional bodyguard "Mr. T" (his real name is Lawrence Tero) as Clubber. He's an unfailing hostile kick. Each threatening glare and spiteful tirade, projected with hilarious deadpan authority, seems to render his Badness all the more amusing.

When "Rocky" was released, Stallone commented, with characteristic self-deprecating humor, that "it's also about my inability to be an actor--set in boxing trunks. I had a feeling that would be more exciting than a story about a struggling actor who comes home, his wife asks, 'How did it go today, dear?' and he says, 'No luck but I got this sunburn on my nose.' " During the same interview he said, "I think I've peaked with 'Rocky'--this is puppy love, the senior prom, winning the homecoming game, and I can't repeat that experience forever."

Since then Stallone has discovered the kind of traps created by success, including the reluctance of an audience to accept a new star in a variety of roles unless he proves so versatile that fans have no other choice. One can imagine Stallone appealing to people in roles other than Rocky, but he still hasn't found or invented those alternatives.