While Walt Disney is playing computer games with "Tron," three renegades from that venerable film factory have come on line with a traditionally animated fantasy, "The Secret of NIMH."

The trio left Disney to crusade for quality in classical cartooning, to recapture the days when dewdrops shone and fireflies pulsed. They burned midnight oil in director Don Bluth's garage to relearn techniques lost with Walt Disney. They shunned all shortcuts. The result is an exquisite canvas of six hundred shifting colors on a thousand backgrounds.

But the story, based on an award-winning novel by Robert C. O'Brien, is another matter. Disney Productions originally turned it down, but producers Bluth, Gary Goldman and John Pomeroy won the rights to the story after their big exit. As it turns out, they should have listened to Disney, for "NIMH" is a glum, liberal-guilt training film.

It's a classic conflict of mice and men, but not of the Beatrice Potter fuzzy-wuzzy school. In "NIMH," a widowed mouse asks a race of Mensa-smart rats to save her row house and four kits from the farmer's plow. The rats, indebted to her husband Jonathan, agree to help mousey Mrs. Brisby (voice by Elizabeth Hartman) penetrate the maze of a plot that has to do with chemical experiments on animals at the National Institute of Mental Health.

Balancing this bathetic Brisby business is Dom DeLuise, the voice of Jeremy, a cockamamie crow who comes on like a Las Vegas lounge singer. It's enough for an occasional cackle, but not enough to offset Mrs. Brisby's stiff upper lip, or the movie's odd morality. It's not that DeLuise isn't up to it. All the dubs are good: Peter Strauss as the Errol Flynn of the rat kingdom, John Carradine as the grumbling Great Owl, Derek Jacobi as a rodent Yoda and Hermione Baddeley as fussy Auntie Shrew.

The creatures are well-drawn and the effects as Druidic as any Merlin might have conjured. There is fiery laser script and a glowing hologram for telling the future. There's also lovely London Philharmonic music (not including a saccharine lullaby by Paul Williams).

Sadly, "The Secret of NIMH" is beautiful but unbalanced: The animators gambled when they should have gamboled.

THE SECRET OF NIMH -- At AMC Academy, K-B Congressional Plaza, Laurel Towncenter, Loehmann's Plaza, NTI Dale Cinema, NTI Landover Mall, NTI Springfield Cinema, Showcase Beacon Mall, Showcase University, Sterling Towncenter, Tenley, Circle, Village Mall, Wheaton Plaza.