NEW YORK >> Composers have long dreamed of bigger orchestras.

In Mozart’s day, when orchestras were small by modern standards, he boasted in a letter of hearing one "with 40 violins" play a symphony of his. Berlioz fantasized about an ensemble with 467 players. And even if it is a bit hyperbolic, there is a reason Mahler’s epic Symphony No. 8 became known as his "Symphony of a Thousand."

But as some American orchestras struggle in the post-downturn economy, they are taking a page from the corporate world and thinking smaller: They are downsizing, shedding some full-time positions while making up the difference with less costly part-time musicians.

The Atlanta Symphony Orchestra ended a contentious labor dispute and a two-month lockout this month by agreeing to a new contract that will effectively keep it smaller for the next few years – placing it in the company of major ensembles in Philadelphia, Detroit, Indianapolis, Minnesota and elsewhere that have temporarily or permanently trimmed their number of full-time musicians in recent seasons to save money. Some are now slowly rebuilding.

Such reductions do not mean that they must become chamber orchestras, or even play their fortissimos with less issimo. But they do require a greater reliance on freelance musicians to play large-scale works by, say, a Bruckner or a Mahler or a Richard Strauss.

Some of the orchestras say they can maintain quality by hiring talented musicians to sit in and note that even major, healthy ensembles use substitutes in the case of vacancies or absences. But musicians warn that an overreliance on freelancers endangers the things that make orchestras great: the cohesion that comes from playing together over many years, the performing traditions that are developed and passed down, even the ability to divine in a flash what a familiar conductor is seeking with a cocked eyebrow or a flick of the wrist.

Michael Kurth, a bassist in the Atlanta Symphony, stirred debate in the music world with a blog post he wrote during the lockout lamenting that his section had dwindled in recent seasons to five players from eight, forcing a greater reliance on freelancers. He wrote that it was like a championship baseball team trying to turn a triple play with a star shortstop who had just arrived from elsewhere. "He may be a phenomenal player, but we’ve been turning that triple play together for years," he wrote.

Some freelancers took exception. But Kurth, who stressed in an interview that he respected their talent, said he had experienced the phenomenon from the other side when, while locked out of his regular job in Atlanta, he was hired as a substitute player with the National Symphony Orchestra in Washington.

"I was that player on the outside, struggling to fit in, and not always sure how to anticipate the conductor," he said.

For many years the story of orchestras was expansionary. Tim Carter, a professor of musicology at the University of North Carolina at Chapel Hill, said that during the 19th century, ensembles expanded dramatically.

"There are three elements which are each feeding off of each other," he said. "Larger performance spaces requiring larger orchestras, which encouraged composers to write music for larger orchestras – which required larger orchestras, which required larger concert spaces."

Orchestra size became a point of contention during the lockout in Atlanta, which ended when the orchestra’s management gave up its unusual quest to drop the requirement for a minimum number of players from the contract and players agreed to let vacancies go unfilled longer.

The result is a smaller Atlanta Symphony, which had become known over the years for large-scale works that showed off the famous chorus formed by Robert Shaw. The Atlanta Symphony, whose contract called for 95 players a few years ago, lowered its minimum to 88 in 2012 – but the new contract will keep it this year at 77, where it has fallen after retirements, deaths and departures, and give it four years to grow back to 88.

It is not alone. The Philadelphia Orchestra’s contract calls for 105 musicians, but while in bankruptcy in 2011 it agreed to a hiring freeze that holds the number of players at 95. The Indianapolis Symphony Orchestra has reduced its size in recent years. And when the Minnesota Orchestra ended a 16-month lockout of its players this year, the agreement said that while its traditional complement of 95 musicians was "optimal," it would have to grow from its current 77 musicians to only 84 by 2017, according to Gwen Pappas, a spokeswoman for the orchestra.

"Our policy has been to hire substitute players as needed for the demands of the repertoire – and concert reviews have been pretty stellar this fall, so it doesn’t seem to be an issue that is noticeable to critics or audiences," she said in an email.

Some well-respected orchestras augment their full-time musicians with other players. The Metropolitan Opera Orchestra, which is widely considered one of the best in the world, has an official complement of 99 players. But since the ensemble’s contract envisions four performances a week, and the Met performs seven, the orchestra bolsters its ranks with musicians who are not full-time orchestra members. Of course, being in a city with a large pool of top-notch freelancers helps.

Robert J. Flanagan, an emeritus professor of economics at the Stanford Graduate School of Business who wrote "The Perilous Life of Symphony Orchestras: Artistic Triumphs and Economic Challenges," said the recent cuts were a reversal of the growth in the late 20th century, when many American orchestras began paying better and growing larger.

"Now, basically, orchestras are trying to change labor from being quite as fixed a cost into a more variable cost," he said.

Bruce Ridge, chairman of the International Conference of Symphony and Opera Musicians, a players’ conference of the American Federation of Musicians, said such cuts were shortsighted. "Our belief is that no arts organization can cut itself to success, and that no business ever solved a financial problem by offering an inferior product," he said.

Some orchestras are bucking the trend. The Dallas Symphony Orchestra’s contract calls for a minimum of 82 players, but the ensemble has long had more than 90. Jonathan Martin, its president and chief executive, said that having a larger complement helped the orchestra to play late Romantic and contemporary repertoire, fostered artistic cohesion, helped attract talent and simply made it sound better in its hall.

"Our consistent practice," he said, "has been that we fill vacancies when they occur so that we maintain that strength."

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