ON SEPT. 13, 1979, evidence of serious discontent within the ranks jolted the apparent institutional serenity of the Disney studio. Three animation directors--Don Bluth, Gary Goldman and John Pomeroy--submitted their resignations, leaving secure positions to form an independent production company. The following day four other animators, four assistant animators and a special effects assistant also resigned. Eventually, this group was joined by five additional Disney defectors and reassembled in early 1980 as the building blocks of Don Bluth Productions, secluded in a new, compact, two-story office building behind a bank on Ventura Boulevard in Studio City, Calif.

Bluth had often been described as the leader of a second generation of feature animators that the Disney studio began to recruit in the early '70s, supposedly with the intention of training them to carry on The Great Tradition represented by classics like "Snow White and the Seven Dwarfs," "Pinocchio," "Fantasia" and "Bambi." In fact, Bluth had worked briefly at Disney as early as the mid-'50s, soon after graduating from high school in Santa Monica. He was an "in-betweener," the term for animators who do the character drawings that must sustain the flow from one key bit of movement to the next.

The departure of Bluth and his associates was the first of several rude awakenings and dismaying setbacks for the once confident Disney organization. The release of "The Fox and the Hound," then in midproduction, was delayed for at least a year while the animation department was revamped and brought back to full strength. New Disney features--"The Black Hole," "The Last Flight of Noah's Ark," "The Devil and Max Devlin," "A Watcher in the Woods"--were proving consistent disappointments at the box office, suggesting that the studio's executives had lost touch with the taste of a family market they had become accustomed to servicing more or less exclusively.

There was also the galling prospect of competition in the proudest Disney genre, the animated feature, from the renegade Bluth group, which had completed a featurette called "Banjo, the Woodpile Cat" and secured the financing for a feature, "The Secret of NIMH." Ironically, "NIMH" was destined to open the same weekend as Disney's "TRON," a science-fiction adventure fantasy combining live action with advanced forms of computer animation. While both "NIMH" and "TRON" were certainly problematic cases, it appeared that Disney was still stuck with a losing streak and the thorniest identity problems.

According to Don Bluth, who discussed the circumstances that led to the formation of his production company in conversations in Washington and Los Angeles prior to the release of "NIMH," the separation could have been averted by a responsive management. "Our pleas fell on deaf ears time and time again," he said. "After the deaths of Walt and then his brother Roy, the place began to be run by committee. The corporate structure got bigger and bigger, and you could see the scale tipping heavily to the business side.

"We kept hearing that we'd have to be satisfied with a new situation that reflected today's economies. Our greatest frustration was that we often couldn't put the effects on the screen that were within our power technically. We assumed the day would come when someone in charge would say, 'Okay, here's your film,' so to prepare for that big opportunity, we'd been training on our own time for years. Gary and John and then several others began spending most weekends at my place, where we set up some used animation equipment in my garage and started working on a short film that eventually became 'Banjo,' five or six years later.

"People thought we used the garage on purpose, because Walt Disney had started in a garage. We weren't that shrewd. We simply couldn't afford anyplace else. My living room had blackout curtains and became the projection room. The family room turned into a camera room, and the editing equipment ended up in the bedroom. The kitchen and patio were the commissary. Any money we had to spare we put into filmmaking equipment because it was literally impossible to practice at the studio. Every piece of equipment there is unionized, and you can't touch it. If we wanted to learn how to do things like shadows or reflections or water effects, we had to learn ourselves through trial and error because that isn't a part of the studio training process. It's precisely those refinements that are in danger of being lost.

"Prospective animators at Disney get a four-week course in pencil sketching. If they pass that, there's another four weeks of pencil tests. If they're accepted, they become in-betweeners for at least a year. For years we were dutifully paying our dues at the studio while working on 'Banjo' weekends and evenings. When we came back with some of the scenes we'd put together and said, 'Look what we can do now!' the reaction was always negative . . . For a long time we were blinded by the magic that will always be associated with Disney's name, but eventually it became clear that we'd make no headway."

Slight and soft-spoken, Bluth (rhymes with Ruth) would not fit anyone's preconception of a firebrand or rebel. He's deceptively bland and unassuming in person, the sort of guy who imposes his authority almost subliminally. Now 44, Bluth was born in El Paso but spent most of his youth in Payson, Utah, where his parents farmed and raised seven kids. The second oldest, Bluth recalls "riding my horse to the movie house in town, where I'd tie him to a tree while I went in and watched the latest Disney film. Then I'd go home and copy every Disney comic book I could find. When I went to work at the studio in 1956, I couldn't tell them I trained myself at home copying their stuff. I just smiled shyly when they talked about my 'natural drawing talent.' "

Bluth left his in-betweener's job in 1958 to spend two years on a Mormon mission in Argentina. Upon returning, he enrolled at Brigham Young University in Provo, the big town due north of Payson, and majored in English. He and his brother managed a little theater in Culver City, Calif., for several years during the 1960s, and Bluth worked as a layout artist at Filmation Studios, doing commercials and Saturday morning cartoon shows before beginning his second, fateful tour of duty at the Disney studio in 1971.

"Since we left," Bluth said, "I think the Disney management has become much more aware. Occasional verbal rocks have been thrown back and forth between us and the Disney lot, but I really think that the fact we're competing should help them create a new studio.

"I was in nominal charge at Disney of a group of the younger guys when we began 'The Small One,' which turned into a terrible mess. Our ages were too close for me to exercise authority over them, and whenever I'd insist on anything, they'd go behind my back and run upstairs. It was about that time that I decided I'd start my own company and it wouldn't be so bad. I made no secret of that intention either. 'Aha, so that's it!' they said. 'Now, we have it. Who are you taking with you?'

"That attitude helped to make it a fait accompli. As it happened, there were a couple of guys on the marketing and administrative side of the company, Rich Irvine and James Stewart, who were nursing grievances of their own and planning to start their own company. They got wind of our plans, looked at the rough version of 'Banjo' and said they thought they could help us, since they had some funding possibilities. And that's what happened. We left to form the animation studio while they left to form Aurora, which arranged the financing for the completion of 'Banjo' and then the production of 'NIMH.' "

At peak periods, Bluth Productions employed as many as 122 people during the 2 1/2 years "The Secret of NIMH" was being made. Shortly before release, the payroll was down to about 65, but the company seemed assured of financing for a second feature, and Bluth was hoping to expand facilities. The production period for "NIMH" seems relatively short for a fully animated feature, which at Disney has been running four or five years from authorization to release. Bluth attributed the speedier work process to "artists putting in lots of extra hours and working their fingers to the bones."

At $7 million, the budget was also pretty much skin-tight. "Everyone's got a profit participation," Bluth added. "That's the only way we could hope to compensate people adequately for the sacrifice and extra effort required. There wouldn't have been a movie if we hadn't agreed to bring it in for $7 million." Just back from London, where he had attended the recording sessions for the musical score, he seemed awed by the contribution of composer Jerry Goldsmith and uncertain of precisely what kind of movie he had on his hands. "At this stage you just hope and pray that it's presentable," he said.

The story, derived from Robert C. O'Brien's children's novel "Mrs. Frisby and the Rats of NIMH," had first attracted Bluth when he was at Disney, which eventually passed on it. "By the time we were ready to start our own shop," Bluth said, "the book had been optioned by two boys from Santa Barbara. Two smart boys, I should emphasize. They picked up the option for $6,000 and obliged us to pay a handsome price for the privilege of filming it. They've done very well off that investment. In fact, I've learned a lot about the business watching them do well."