Napster Inc. begins selling MP3s Tuesday, a move the online music service hopes will lure iPod users and turn around Napster’s sliding fortunes.

The company is the latest to make the switch to the unrestricted file format, which makes it music tracks compatible with virtually any music player or other device.

“It’s great that we have finally gotten here,” said Chris Gorog, Napster’s chairman and chief executive. “It is really the beginning of a level playing field, which I think is essential for Napster, but also for the health of the digital music business in general.”

Tracks downloaded as part of Napster’s subscription service will continue to have copyright restrictions.