"Rocky II," opening today at area theaters, doesn't merely recall its Oscar - winning predecessor, a modestly produced but astutely calculated inspirational fable about the rehabilitation of a dow - and -outer. It slavishly repeats the plot of "Rocky," achieving differentiation only in dubious forms: soap opera detours, delaying tactics and an ugly new mood of viciousness surrounding a rematch between the boxers.

The sequel commences with a rerun of the frenzied closing scenes fromm "Rocky": the last round of the original fight between Carl Weathers as Apollo Creed, the cocky black champion, and Stallone as Rocky Balboa, the motley Philadelphia club boxer given a fluky shot at the title; the announcement of the split decision won by Creed; and the final embrace and exchange of "I love you's" between Rocky and his girl Adrian, played by Talia Shire.

The dramatic material in "Rocky II," written and directed by Stallone, kills an hour and a half of screen time between the old fight sequence and a new one, designed to top the original by being longer and bloodier and ending more preposterously.

For a brief period it appears as if Stallon's offbeat humor might sustain the continuation. Transported by ambulance to the hospital immediately after the fight, Rocky seems ot be in good form answering the questions of a clamorous sporting press. "What was the first thing that crossed your mind after the fight?" inquires one scribbler. "That I shoulda stayed in school," Rocky thoughtfully growls. "Do you think you've got brain damage?" another reporter asks eagerly. "I don't see any," Rocky replies. Taking leave of Adrian before entering the operating room, Rocky further endears himself by observing, "You better go home. I'm gonna be busy here healin' for a while."

But the new scenario begins to degenerate into a tedious and alienating rehash as soon as Rocky is patched up. Adrian and Rocky marry and move into a new townhouse, but it doesn't point the film in a fresh direction. Adrian is still limited by Stallone's inability to write dialogue for his leading lady. At the same time his improvisations for himself start to get so cute that they're downright annoying.

During the wedding and house-hunting scenes Stallone undermines Rocky's likability by slipping into smarty-pants caricature. He hogs the lines and the business more than he should. It's apparent that Stallone has slicked up and essentially falsified the character, imposing a joky, self-aware image on what began as a sincere impersonation of a lovable brute.

Despite the changed attitude toward the character, however, "Rocky II" has only one aim: to get Rocky and Apollo back in the ring. Given their characters as depicted in "Rocky," it's unlikely that either boxer would relish a rematch. Stallone chooses to ignore the obvious financial motives that might lead to a second bout. Playing it underhanded, he tries to convince us that Rocky has become more of an underdog than ever while Apollo has changed into a villainous fanatic.

Rocky leaves the hospital supposedly determined to give up boxing since his right eye has been damaged. Incredibly, he is shown to be a flop at televised commercial endorsements, suffering humiliating abuse at the hands of an irritable director.In real life, of course, Rocky and Apollo would have been amicably rematched in an infinite number of commercials, but never mind real life. Poor Rocky slides down the social ladder will he's back doing janitorial work at the gym run by his former trainer Mickey, again portrayed by Burgess Meredith.

Meanwhile, a pregnant Adrian has been forced to return to work in the pet shop. Her brother Paulie (Burt Young again) has inderited Rocky's old job as collector for loan shark Gazzo (Joe Spinell again). The vengeful Apollo has begun a smear campaign ludicrously calculated to provoke Rocky into a rematch, branding him "the Italian Chicken."

Reluctantly; the Rock agrees to accept the challege and subjects himself anew to Mickey's rigorous training and frightful nagging.Half-hearted, Rocky neglects training totally after Adrian sinks into a coma upon giving birth prematurely to their first-born, Rocky Jr.

Adrian's coma relieves Stallone of the obligatoin of writing dialogue for the heroine, a shy thing to begin with. Like Streisand in "A Star Is Born," he luxusiates in self-pity, lingering over scenes of Rocky maintaining a tearful scenes of Rocky maintaining a tearful vigil at Adrian's bedside or in the hospital's chapel. To comfort his unresponsive beloved, Rock reads aloud from Edgar Rice Burroughs and a poem of his own composition. I'd give more than a penny to hear the thoughts that ran through Talia Shire's head while she played unconscious for these mawkish demonstrations.

Rocky's devotions are rewarded: Adrian stirs, awakens and tells him, "There's one thing I want you to do: Win " This resurrection cues a reprise of the Rocky-in-training production number, now embellished with a corps de ballet of tykes who miraculously keep pace with him as he repeats all that picturesque roadwork on the streets of Philadelphia.

Overcompensating like crazy, Stallone whips up a frenzy around the rematch that transforms it into a vicarious race war. Apollo, allegedly stung by the thought that he couldn't whup a white turkey, enters the ring lusting for blood. In the other corner Mickey of the Rocky-in-training production bloodlust can't help but rub off on Rocky, although Stallone may not have intended it to. By that time things are too far out of hand, including Meredith's egregiously nasty, nutty performance, while the director of record evidently declined to control.

The second fight is a pretentious, attenuated set piece of head-snapping, ear-splitting haymakers, culminating in a double knockdown with a slow-motion race by the woozy gladiators to struggle up before a very long count of 10.

Probably it will play. Heaven knows it has to or else oblivion is just around the corner for Sly Stallone. Nevertheless, it's an absurd charade from the opening punch, which indicates that Apollo isn't very inconvenienced by Mickey's crafty strategy of turning Rocky into a right-hander.

The surest indication of how desperate Stallone has become is the startling change in Adrian on fight night. Watching at home on television, even dear little Adrian begins screaming for Rocky to beat his opponent's brains out. Vaguely, one recollects something about her concern for Rocky's health if he stepped in the ring again, but all that seems far away by the time "Rocky II" collapses into a fadeout.

Stallone appears so anxious to retrieve his quickly squandered popularity that when the sweat flies off his brow, it might as well be flying off the screen to shower the audience. To make matters worse, he has sprinkled this grotesquely manipulative come-back movie with so many speeches in which Rocky humbly invokes or thanks his good pal, God Almighty, that you begin to suspect the star may be confusing his sweat with holy water.

If the public Stallone desperately wants to please again elects to humor him, it could prove a self-defeating indulgence on both sides, provoking a "Rocky" series in which the hero and Apollo Creed contend for the title until both are mercifully retired to the Old Pugilists Home. Stallone might end up paying one role for the rest of his career - but he'd better play it for laughs. CAPTION: Picture, Carl Weathers, left, and Sylvester Stallone in 'Rocky II'