Apple Computer has unveiled an adapter that lets users of its iPod digital music player connect them to stereo systems in some BMW and Mini Cooper models and use buttons on the steering wheel to play their music libraries.

Apple and BMW said the adapter, priced at $149 (U.S.), would work in BMW's 3 Series, Z4 Roadster, X3 and X5 SUVs and the Mini Cooper, and will be powered by the car, not the iPod's battery.

Drivers plug the iPod into a cable in the car's glove compartment and then can control the iPod using the standard buttons on the steering wheel.

Some new cars already have audio jacks that can be used to connect digital music players, including the iPod, to car stereos, and devices using a car's power outlet and a cassette player or a small radio transmitter are available. However, many new cars no longer have cassette players.

But Apple said this was the first time that an adapter had been specifically designed to integrate the player with the existing audio controls of a particular car model.

"This is the first really big step that's been taken to marry iPod to automobiles," said Steve Jobs, Apple's chief executive. The Apple-BMW agreement is not exclusive, which means Apple tie-ups with other auto makers could follow.