THE MUSIC lurched and so did the scene - broomsticks, endless lines of them stretching out of sight, each magically endowed with two arms, carrying a pair of waterfilled buckets and marching toward a panic-stricken Mickey Mouse, adding to the flood that threatened to drown him.

This scene from the "Sorcerer's Apprentice" episode in "Fantasia," marked the dawning of a new realization for most Americans: the unlimited power of the animated cartoon.

It happened later in "Bambi" and again in the "Pink Elephants on Parade" sequence in "Dumbo." At the core of the experience was the intoxicating sense that anything can happen on that screen: An army of broomsticks can carry enough pails of water to make a flood; an elephant can be transformed before your eyes into a cobra, a belly dancer, a racing car. Unlike a cameraman, the producer of an animated film has full control of what happens on the screen - and full responsibility.

For most Americans, no matter when this effect first happened, the odds are that the material that produced it was first put on film in the 1930s.

"That's when animation had its golden age - less than 10 years," according to J. Michael Barrier, a historian of animation who wrote the catalogue for the exhibit. "To Build a Better Mouse," now showing at the Library of Congress. "If you're interested in animation as art, you have to dig into its past or hope for its future, because it isn't happening now."

Of course, in terms of sheer quantity, animation is happening now as never before. There are waiting lines in Washington for two full-length animated films, Martin Rosen's "Watership Down" and Ralph Bakshi's "The Lord of the Rings," and reports from Hollywood say that we can expect more in the near future with such heroes as Superman, Flash Gordon, Dick Tracy and Popeye. And on television any Saturday morning, animation is whiz-bam popping out of the screen at a frenetic pace.

But the pace is part of the problem, it excludes opportunities for fine detail and the play of imagination - qualities that distinguish art from mass-produced entertainment. And despite the enormous output, recent animated features have met with critical yawns, and the most promising projects seem disappointing.

Barrier explains one reason why: "In the Disney studios at the peak in the 1930s, one of the great animators might turn out 3 feet of film per week - a few seconds on the screen - with no raised eyebrows. The average then was 20 to 25 feet per week. Today, at the big television studios, 150 feet per week is typical - which is one reason why so much of the real action takes place off the screen."

Since studios began producing animated films regularly 65 years ago, most technical improvement were not technical breakthroughs, but refinements, based on willingness to try harder and spend more money.

In recent years, that willingness has disappeared. And new techniques - the capability of photocopying a drawing directly from paper to transparent celluloid, for example, which eliminates the middleman in the anination process - have arisen to reduce costs.

"Taking shortcuts is all right," says Barrier, "as long as it doesn't affect the artistic result. Disney took shortcuts where it didn't show. But today, shortcuts are the goal."

In fact, shortcuts may be the only way you can produce an animated feature today without going broke. "Snow White," which cost $1.7 million, and "Fantasia," which cost $3 million to make in the 1930s, would cost many times those amounts today - even using modern techniques that have cut in half the number of man-hours needed for an animation. The Disney studio now has two major animations in the works. "The Fox and the Hound," scheduled for 1980 and budgeted at $10 million, and "The Black Cauldron," which will be brought out in 1984 at a cost of about $15 million. Last year's feature animation, "The Rescuers," proves that there can still be big profits in animated features - at least when they bear the magic name of Disney. Produced at a cost of $7 million, it grossed more than $30 million in its first year.

"Watership Down" (which cost over $7 million) and "Lord of the Rings" ( $8 million) both cost far more than "Snow White" or "Pinocchio" and fall far short of them in terms of detail and realistic animation. Each of these films seemed to have everything going for it. They were based on books with large, enthusiastic readerships, they had to be filmed to satisfy public demand, and neither could have been filmed except through animation. Their seeming failure to meet the Disney standard of the '30s is a failure of the industry as much as of any individual and the reasons are largely financial.

In animation, artistic quality and budget are virtually equivalent. There are expensive technical standards that apply uniquely to animations: Do the figures move naturally and gracefully? How detailed are the scenic backgrounds and facial expressions? Does a speaker's mouth move differently when pronouncing an "o" and a "p?" Do the eyes move, and is there knee-action? Does the bodyshift its position subtly from one moment to the next as a living body does?

And there are other, more sophisticated criteria. The number of characters in a scene, for instance, it is much more complicated to animate a scene in which half a dozen characters are moving in varied ways than a scene with only one or two characters. In Saturday-morning television animations, the typical scene has only two characters - and a good part of the time, only one of them is moving. Sometimes the top or bottom of a character will be in motion while the rest is unrealistically immobilized. The fewer changes there are from one frame to the next, the lower the expense will be.

Some studios got around the expense of animation by abandoning the goal of realistic effect entirely - Jay Ward, for example. In his television program, "Rocky and His Friends," the attraction was not good animation but good writing, interesting story lines and bright dialogue. It had been called "radio with pictures." It is also less expensive to use the actors' voices rather than the pictorial effect for characterization, so you see a lot of animation with interesting voices coming out of uninteresting pictures.

In "Watership Down," the rabbits don't look furry because furry rabbits would be a lot more expensive to animate than rabbits that look like they are made of cloth. Expenses also are reduced when the scene shifts, as it does fairly often for sequences dealing with dream or legend, into a sort of abstract style. All attempts at realism are abandoned and the rabbits become immobilized silhouettes, sometimes against a nonscenic background of pure color. In one respect, the subject-matter helped keep down costs; abrupt, jerky movements typical of rabbits are a lot easier to animate than smooth, graceful movement.

Cost-cutting for "Lord of the Rings" was done by shooting the film with live actors and then tracing the animation over the figures already captured on film (the movie's director, Ralph Bakshi, calls this process "moving painting"; there also is a more old-fashioned and less dynamic term: "rotoscoping.")

Barrier points out that this is not really a new idea: "When 'Snow White' was nearly ready, they wanted to get it finished and keep the costs down, so they shot and traced the role of the prince in the same way - which may be one reason why the prince is the least vivid character in the picture. If that were a good way to do animation, it would mean that the highest form of art is tracing a photograph. Realistic motion for a human actor on film is not the same as realistic motion for an animated character."

The budget problems that assailed "Lord of the Rings" are particulary evident in some crowd scenes, where the animation is so lightly applied that you can clearly see the human actor underneath the figure of the animated ore or human being.

Both films also face another, almost insuperable problem: the difficulty of matching images with imagination. Anyone who has read Tolkien probably has an image of a balrog that is less defined but more terrifying than the balrog in the films, which looks something like King Kong equipped with bat-wings. The necessity of making a picture - of limiting the imaginative possibilities with a concrete image - is the most serious problem an animator faces and one that transcends questions of pure technique. Every Tolkien fan has a mental picture of Frodo, of Gandalf, of what an elf should look like. Disney at his best would have been more impressive that the film that is not showing, but he could hardly have satisfied such expectations.

Even a graphic genius who might be able to fulfill everyone's visual expectations would still have trouble, however. Without a budget that would make studio executives cringe, it simply is not possible today to produce the fantastic grandeur of vintage Disney. With each passing year, his productions of the 1930s seem more and more unattainable - the product of a brief period in motion picture history that probably cannot be brought back again.

The standard studio technique dating from the early years involves the painting of a background scene and then overlaying it with figures painted on transparent celluloid (called "cells") for each successive frame. Figures that are not moving become, in effect, part of the scenery: a cell is laid in place and left immobile for as many frames as the character stands still. Sometimes parts of a charater's body that are not moving become temporary parts of the scenery, while other parts (the face, for example) continue to be animated with changing cells. Sometimes, three or four cells are overlaid simultaneously on a single background.

The first major addition to this technique was the introduction of sound. Disney's "Steamboat Willie" (1928) was not quite the first animated cartoon with sound (a few others had added sound to silent cartoons), but it was the first in which the movements of the characters were synchronized with the sound. A few years later (1932), Disney began to use color, and he was so successful where others had hesitated or failed that he was given a two-year exclusive franchise for the use of Technicolor in animation.

Exploiting this technical advantage in the early '30s, Disney expanded his staff rapidly (in the Depression, a lot of superior artists were readily available), and preliminary work on "Fantasia" began in 1930 - seven years before the picture was released. Among the cartoonists who worked for Disney in this period were Walt Kelley (creator of "Pogo"), Virgil Partch ("Big George") and Hank Ketcham ("Dennis the Menace").

With the expansion of staff and the proliferation of projects, specialization also arrived. Senior animators began to draw only the "extremes" - the key drawings that define the shape of a particular motion - and assistants were hired to do the "in-betweens," which make the action smooth and complete. Animators were chosen for their sense of motion, and the assistants were frequently better draftsmen. Besides tracing the animators' sketches from paper to transparent celluloid, they would clean up the rough lines dashed off by the animators in the heat of creation. In the beginning, they also sketched backgrounds to be done by a specialized background-painter, but later backgrounds were turned over entirely to a separate department.

"By the end of the 1930s," according to Barrier, "Disney had assembled a staff that could do anything he asked it to in animation. I think that Disney may have been on the verge of making animation an adult art when he ran into a stone wall: World War II.

"During the '40s, a lot of artists from the Disney studio scattered to other studios that were making animated cartoons. Looking at their work from this period, you can see how they improved the standards of animation or draftsmanship at their new studio, but you also get the feeling that the artist feels lost, away from the Disney environment."

The war cut off Disney's technical growth by cutting off the funds that nourished it. By the time "Pinocchio" and "Fantasia" were ready for international distribution, the war was on and foreign markets, which produced half of Disney's revenues, were cut off. "Pinocchio" lost $1 million on its first run. "Dumbo" was rushed out in a hurry and on a low budget (you can tell, if you look closely at the amount of detail in the backgrounds, for example) to recoup some of the losses on "Pinocchio" and "Fantasia," and it made a handy profit, but it marked a step backward technically. It was the first feature-length film in which Disney had to compromise seriously to make the bottom line come out right, and it set a pattern for postwar productions ("Cinderella," "101 Dalmatians"), which are technically competent and entertaining but do not aspire to be adult works of art.

The only hope for a revival and development of animation as serious art is that sooner or later someone may arrive on the scene with the capital to do it right and the patience to wait long enough for the results to justify the expense. A well-made animation seems to have an indefinite life-span. "Pinocchio" may have lost a million on its first run, but it has been brought back repeatedly since then for tremendous profits, and it will probably still be making them 40 years from now. What the art of animation needs is a producer who is willing to do it right in the hope that he will still be able to make people wait in line in the year 2018.