"The Champ" has personality resources that give it a better chance than most of the tear-jerking competition. Indeed, if it were content to be a heartwarmer built around the obvious rapport between Jon Voight and Ricky Schroder, an 8-year-old prodigy at evoking pathos, it might have breezed home.

Unfortunately, "The Champ" does not let well enough alone. It slogs on for about two reels too many, concluding on a note of utterly contrived tragedy that should make just about everyone feel wretchedly deceived.

Audiences who warm to the illusion of Voight as a loving father and Scroder as his adoring son are likely to be more annoyed than devastated by the underhanded plot twisting that leaves the child in the care of his negligent mother, portrayed by the reigning Queen of Tics herself, Faye Dunaway.

Voight plays an ex-pug, a former prizefighting champion now employed as a handler in the stables at Hialeah Park in Miami, where his kid happily works, plays and soaks up track savvy. Ironically, it's Voight who look robust and alert and Dunaway who looks over-the-hill and punchy.

The Dunaway character ditched the fighter and her son when the child was still an infant. She turns up as a prosperous fashion designer, married to an amiable sort, Arthur Hill, who later identifies himself as a gerontologist, and friendly with an effusive horse owner played by Joan Blondell. When Dunaway first encounters Ricky Schroder in the paddock, she doesn't even realize he is her own wee reject.

When she discovers, the connection, repressed maternal vibes are stirred, but they seem to play weirdly discordant tunes on Faye Dunaway. Perhaps she's never had much contact with children in real life. Something must explain the way she transforms this character's awakened maternal guilts and longings into a sidesplitting spectacle of yearning pantomime.

When Dunaway feels moved to cuddle up close to the boy, she suggests no one so much as Dracula taking aim on a succulent neck. Her affectionate overtures are so hilarious that they really deserve a screwball comedy to rationalize them. At one point she panics the kid into an understandable fit of hysteria, a Ricky Schroder specialty. She prepares what appears to be a mustard and mayonnaise sandwich on white bread for the child, who declines this absent-minded taste treat with fear clouding his ordinarily bright blue eyes.

Dunaway's character doesn't force a custody battle. She just craves a little childish companionship. As she tells Voight, "You're so lucky . . . God how he loves you! I'm a woman who suffers and wants her child to accept her as a mother!"

Although this confession ought to make the hero regard his ex-wife as strictly no competition, he fails to catch on, being an uncerebral lovable brute. The unhappy denouement is triggered not by a custody battle but by the hero's unjustified inferiority complex about his ex-wife's wealth. Picking up the boy at her block-long yacht, the boxer is so depressed at the sight of all the costly gifts the kid has accumulated that he hides his own gift, a big panda won at a shooting gallery. In fact, he drops it on the pavement surreptitiously, so that only we can see and exclaim, "No, Pop, not the panda!"

After tormenting himself on this score for some time, the hero decides that only a ring comeback will allow him to provide for the boy in a style commensurate with mom's. It proves a miserable decision for everyone concerned. Following one of those outlandishly punishing prizefights that the movies have a copyright on, with the opponents landing about 10,000 haymakers each until one sags to the canvas, the story takes the count too, expiring all choked up for no sufficient or inevitable dramatic reason.

I haven't seen the original version of "The Champ," a tear-jerking hit of 1931 directed by King Vidor with Wallace Beery and Jackie Cooper as the boxer and the kid. Friends who have testify that Franco Zeffirelli's remake follows the original plot faithfully, updating only the setting and expanding the mother's role in an effort to make it more sympathetic.

Voight has to be more convincing as a boxer than Beery was, and I suspect he's more convincing as a well-meaning father as well. He tries to give the role an eccentric originality within the pug tradition. His first appearance is wonderful, doing a kind of impromptu roadwork dance as he leads a horse out of the stables. Blond, tow-headed Ricky Schroder looks enough like Voight to pass for his son, and you can feel their pleasure in every scene that has an improvised mood.

Voight and Schroder make it unnecessary to strain for an affecting father-son relationship. Nevertheless, Zeffirellie seems to have carried over a surfeit of would-be heartbreaking cliches, situations, reflexes and dirty tricks from the original. Vidor's movie was probably excessive, but its morbidly despairing sentimentality may have grown organically out of slummy Tijuana settings and a Depression ambience.

Zeffirelli's version tries to match pretty color and a nominally contemporary setting with unmitigated '30s sentimentality. The incongruities can get a little absurd. For example, when Voight drunkenly moans, "What kind of father am I? I stole $20 from my own kid!" and Schroder replies, "That's okay, Champ, my money is your money," one can almost hear Berry and Cooper speaking the lines.

In another respect, it's amusing to see Hialeah transformed into a vision in pink on Zeffirelli's whim-it's as if everyone at the track has heeded the command of Kay Thompson in "Funny Face" to "Think Pink!"-but the decorative inspirations tend to clash with the dismal drift of the show.

Ultimately, "The Champ" relies on traumatizing a kid to achieve its emotional effects, and the ruthless nature of the manipulation is distasteful. It's as if everything depended on a child actor's ability to imitate hysteria when confronted with the possible loss of a parent. Schroder is a little virtuoso, and evidently Cooper was too, but the dramatic justification for their virtuosity is so feeble that one leaves vaguely despising the filmmakers.

What accounts for the proliferation of largely unsatisfying tear-jerkers over the past year or so? "The Champ" was preceded by "Ice Castles," "Uncle Joe Shannon," "Momen by Moment," "Oliver's Story," "Slow Dancing in the Big City," "International Velvet," "If Ever I See You Again" and "The Other Side of the Mountain, Part II." Other examples have yet to reach town. Movies about teen-age gangs may loom a threat to some people, but if anything ails American movies at the moment, it's a plague of weepies. CAPTION: Picture, Jon Voight and Ricky Schroder in "The Champ."