Tradition imposes a special burden on the Disney studio when it comes to animated features. Although the form is too costly and exacting to encourage competitors, the studio must live up to its own glittering inventory. Measured against a 40-year heritage of Disney classics, from "Snow White and the Seven Dwarfs" through "The Rescuers," the studio's new animated feature, "The Fox and the Hound" seems a dinky, lackluster offering.

Opening today at area theaters, "The Fox and the Hound" traces the enduring friendship between a fox clled Tod (short for "Toddler") and a bloodhound called Copper who become playmates as pups and eventually transcend a mortal enmity cultivated by Copper's master, a mean-tempered hillbilly named Amos Slade. The exposition tends to settle into a low-key reverie, reminiscent of "Bambi" but weakened by the failure to create fresh characters and episodes of comparable charm. If anything, "Fox" demonstrates an ill-advised fondness for the most dubious aspects of "Bambi," including its ickily coy approach to animal mating, revived here when Tod is given a breathy, fluttery-lashed girlfriend called Vixey, whose demure lines have been entrusted to Sandy Duncan.

The languorous, saccharine tendencies need plenty of comic resistance. Unfortunately, they get little. "The Rescuers" sustained a suspense plot enhanced by a wealth of comic incidents, characterizations and throwaway gags. "Fox" tries to get by on a pinch of humor. Comic relief is represented almost exclusively by a tedious running gag in which two goofy birds attempt to catch an elusive caterpillar. A marginal joke for marginal characters, it provides a fleeting bit of distraction from the prevailing droopiness.

The only effective contrast is provided by scenes of emotional loss or terrifying peril. While "Fox" lacks comic vitality, it certainly duplicates another vintage Disney specialty, inspiring sobs from real toddlers at the depiction of a wee creature deprived of his mother. Like Bambi, Tod is orphaned when his mother is killed by hunters. Prompt maternal substitutes appear in the form of an owl called Big Mama, a role spoken by Pearl Bailey no less, and a lonely farm woman, the Widow Tweed, whose property is located next to the ornery, trigger-happy Slade.

The best-sustained sequence is a concluding epic struggle in which Tod and Copper, initially pitted against each other, reunite to fight a ferocious grizzly. The graphic excitement of this battle is increased by the fact that it seems to emerge so suddenly and belatedly from such a bland context. Unlike "Watership Down," which may have influenced the Disney group to a certain extent, "Fox" doesn't have a story that seems to be conceived along epic martial lines from the very beginning. At its most characteristic, "Fox" is a softie. Things certainly pick up when the animals begin fighting tooth-and-claw, but the switch in tone comes as a shock. Parents who regard the action sequences in "Raiders of the Lost Ark" or "Dragonslayer" as excess stimulation for juvenile eyes are perhaps even more obliged to deplore "The Fox and the Hound," since the only good stuff is the frightening stuff, and it tends to come out of nowhere.

Of course, it's the rare effective children's movie that doesn't succeed in scaring kids in one way or another.Even a comic context may be no protection to a kid too young to understand the outrageousness of the threat. For example, the campy villain of "The Rescuers," Madame Medusa, tended the scare the daylights out of little kids while she was amusing big kids and grown-ups. One of the choicer ironic scandals in movie history was the rejection of the witty musical fantasy "The 5,000 Fingers of Dr. T" back in the mid-'50s after mothers expecting Something Nice from the first movie written by the trusted Dr. Seuss discovered that their kids were terrified by Hans Conreid's Dr. T, a little boy's nightmarish exaggeration of his officious piano teacher.

"The Fox and the Hound" seems to come alive when it discovers ferocity, but the discovery would surely seem less gratuitous at the climax of a scenario that sustained suspense and always promised high adventure. "Fox" acquires melodramatic bite a little too late, and even then the bite remains tentative. Given its recent string of tepid, misbegotten releases, the Disney studio needs an attraction considerably more beguiling or compelling than "Fox" to snap out of the doldrums. Now that the lag between new animated features approaches four to five years, the Disney people face a long dry spell if they fail to excel at the form perfected by the founder himself.