Signaling another departure from the music industry’s longtime antipiracy strategy, the Universal Music Group will sell a significant portion of its catalog without the customary copy protection software for at least the next few months, the company announced yesterday.

Universal, the world’s biggest music conglomerate, said it would offer albums and songs without the software, known as digital rights management, through existing digital music retail services like RealNetworks and Wal-Mart, nascent services from Amazon.com and Google, and some artists’ Web sites.

But the music will not be offered D.R.M.-free through Apple’s iTunes, the leading music service. The use of copy protection software has become a major bone of contention in the digital music business, where iTunes accounts for the vast majority of download sales. The record labels generally have required that retailers place electronic locks to limit copying of music files.

But Apple’s proprietary D.R.M. does not work with most rivals’ devices or software — meaning that music sold by competing services cannot play on Apple’s popular iPod. Some record executives say they believe that the stalemate has capped the growth of digital music sales, which the industry is relying on more heavily as sales of plastic CDs slide.