In the final moments of The First American Cello Congress at the University of Maryland, the orchestra of 200 cellists had joined the audience in the applause. They stood up and clapped rhythmically for cellist-conductor Mstislav Rostropovich, the charismatic leader of the final concert and of the entire four-day congress. Rostropovich, coming out for what must have been his dozenth bow, picked up a cello (the one belonging to Leslie Parnas) and held it up to take the applause as the symbolic star of the evening.

This was precisely the right gesture to climax four days of intensive discussion and performance focused on the big stringed instrument whose English nickname, ironically, is an Italian suffix meaning "little" (the formal name, violoncello, means "little bass viol"). It ended a concert whose first half was played by an orchestra composed entirely of 200 violoncellos, which were joined by eight bass viols, seven harps and timpani in the second half. It was the largest cello orchestra ever assembled, and it produced sounds that no human ear had ever heard before--including the world premiere of a new composition by Lukas Foss: "200 Celli: A Celebration," whose name describes its mood and the forces needed to play it.

"It will sound like The Attack of the Killer Bees. Cello ensembles always do," a young cellist had predicted before the first rehearsal. He was partly right; there was intense buzzing right at the beginning, but it hardly dominated the music's flavor. There were also deep, rumbling motor rhythms and chromatic harmonies to identify it as a modern work.

Fragments heard in an early rehearsal had evoked many other sounds: lions roaring in a jungle, perhaps, or footsteps through dry leaves, a spaceship entering the outer atmosphere or a pet shop full of demented canaries. Mostly, though, these fragments sounded like music by Lukas Foss: permutations on a matched pair of rising and falling three-note motifs. Last night, when the various segments played by the orchestra's 10 sections were put together for the first public performance, the fragments of sound coalesced into an ensemble of incredible richness.

The prevailing sound conveyed a sense of enormous depth in a performance that used great power with great delicacy. In the orchestra, amateur cellists mingled with some of the world's greatest performers on the instrument. They blended smoothly in the final performance and played with a special fervor--partly because this was a very special occasion for them and partly because Rostropovich, generally recognized as the leading cellist of this generation, was the conductor.

Strictly speaking, the Foss work was not the best music on the program. That was the Bachianas Brasileiras No. 1, composed by Heitor Villa-Lobos for eight solo cellos and performed by an ensemble that included some players who are internationally famous and some who are merely very good: Leslie Parnas, Sharon Robinson, Nathaniel Rosen, Carter Brey, Mihaly Virizlay, Evelyn Elsing, Jeffrey Solow and John Martin. The Villa-Lobos study in solo cello textures, beautifully idiomatic for the instrument and expressed in lively, intricate forms, contrasted neatly with the Foss study in massed cello textures. The rest of the program was made up of simpler works whose effect was greatly enhanced by the orchestra's superb tone and discipline: the Sardana of Pablo Casals, the Entr'acte from "Raymonda" by Glazunov, and Davidoff's "Hymne."

Music was only part of what went on at the meeting that included workshops and panels on a wide variety of topics, as well as concerts of relatively unknown cello music. At one session, cellist Stephen Kates looked out at the audience and began meditating on numbers. "If each of us in our careers trains 10 wonderful students," he asked them, "and each of them trains 10 more, how many cellists will there be by the year 2000?"

After three days of the congress, Question No. 1 was on the table: the question that had been on everyone's mind but nobody seemed anxious to bring up because nobody knows the answer. It is a question that could also be applied to virtuoso pianists or string quartets, oboists or flutists--the question of supply and demand. In the last generation, America has been transformed from a country that had to import most of its classical music and musicians into a land with a serious surplus of excellent performers.

"As a teacher," said one cellist in the audience at a panel session yesterday, "I am frightened. I know that there are hundreds of applicants for every orchestral seat--and either you make it to the top shelf or you starve." The 400 cellists who assembled in Maryland are acutely aware of this; they are the ones who must struggle for a limited number of orchestral positions, solo engagements or concert dates.

At their meetings, and in the informal gatherings in lobbies and lunchrooms, there was a special air of camaraderie--the affinity of people who share a common obsession and who delight in the fellowship of colleagues. The air was thick with technical shop talk about repertoire, teaching techniques, the design of cello bows and related topics. A shop set up in the lobby of the university's Adult Education Center was doing a brisk business in peripheral material of interest to cellists: sheet music and cello strings for business; T-shirts and tote bags with pro-cello slogans for recreation and propaganda. A bulletin board listed impromptu activities and special concerns ranging from "Cello for sale" to "Special Meeting: Orchestra Audition Strategy (what repertoire, etc.)." And there it was again; these people who were so spontaneously friendly and interested in one another were also in intense competition.

Nobody seemed to like the idea, even those who have made their way to the competitive top. "We must face the fact," said Stephen Kates, "that there is a business--a very large business--dominating what we do when we call ourselves artists."

Zara Nelsova told of how she took an orchestral job in Toronto at $15 a week and saved up her pennies until she could afford a debut recital at Town Hall in New York, after which "the reviews were wonderful and absolutely nothing happened"--so she went back to Toronto, quit her job and began the long, hard route of the cello soloist anyway. "Unless you have faith in yourself and you love what you do, with no thought of return, you will never accomplish anything," she said.

Orlando Cole, who was one of the founding members of the Curtis Quartet in the 1920s, recalled that the competitive situation was even worse then. "There were only about 200 people in the audience at the first Casals recital in the United States," he said, "most of them fellow string players. After Piatigorsky made his debut with the Philadelphia Orchestra, playing the Dvora'k Concerto in 1929, there was nowhere else for him to play but women's clubs. Then, when Feuermann came on the scene, there wasn't really room in the United States for two cellists and it was a struggle. If you did 20 concerts in a year, that was a good season." In 1909, when his father was a violinist with the Philadelphia Orchestra, he recalled, there were so few American orchestral musicians that rehearsals were conducted either in French or in German, depending on the conductor.

Since then, the cello, like other classical instruments, seems to have become almost a victim of its own success. But in this case, the victims are beginning to organize. A movement was launched yesterday to have everyone at the congress sign a petition favoring government support of the arts; a committee was organized to come to terms with airlines that make cellos fly in a passenger seat with a paid ticket; and, most momentous of all, the first national organization of and for cellists, the American Cello Council, was officially founded. The First American Cello Congress already has two sequels scheduled: next year in California, hosted by the California Cello Club, and in 1984 at the University of Arizona in Tempe.