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.