Social networking MySpace on Thursday launched a new service allowing visitors to listen for free to millions of songs.

The service, known as MySpace Music, comes as the embattled music industry looks for ad-supported streams of revenue to make up for declining sales of traditional music media like CDs and albums.

The service includes songs that make up the catalogs of the four largest record labels in the world.

MySpace users now can search for a song by title, artist or album, select a track to add it to a playlist, and listen to it using an on-line music player.

Ads appear on the player, and tracks on the playlist link to Amazon.com's music store, where users can purchase them for download.

MySpace revealed the formation of MySpace Music in April and said at the time that it would be a joint venture between the social networking site and three major labels: Sony BMG, Universal Music and Warner Music.

MySpace Music has added a fourth label, EMI, independent music distributor the Orchard and Sony ATV, which owns the rights to the Beatles songs.

Steve Pearman, MySpace's senior vice president of product strategy, said that while MySpace Music is certainly not a cure- all for the music industry's woes, it provides a platform to experiment with revenue models.

"If you want to listen to tracks, you should be able to listen to tracks," he said in remarks published by the San Francisco Chronicle on Thursday.

"Let's give users what they want, and then we'll figure out what the business model will be. You can build a real business by setting music free," he said, adding that he thought the service would compete well with illegal peer-to-peer sites.

Pearman said MySpace Music would add to the social networking site's community-building features (users will be able to share play lists and post them on their profile pages) and build traffic.

Pearman declined to provide goals for revenue or traffic. But he said 35 million of the roughly 75 million unique hits that MySpace gets each month are generated from the social network's music pages.

Several major advertisers, including McDonald's, Sony Pictures, State Farm and Toyota, already have signed on.