Chrysler Corp. has demonstrated the world's first public deployment of a driver's side air bag in a minivan, saying it will offer the safety device to buyers at no extra cost beginning early this year.

During a preview at the North American International Auto Show in Detroit, Chrysler President Robert Lutz deployed the air bag by pushing a button as a company engineer sat behind the wheel."This is the first air bag system built into a minivan or light truck," Lutz said before the bag inflated with a loud bang.

Among U.S. automakers, Ford Motor Co.'s Aerostar van will most likely be the next minivan to be equipped with an air bag, sources said.

Chrysler will offer the balloonlike safety device at no extra charge, or in conjunction with anti-lock brakes for $499. Chrysler's minivan models include Dodge Caravan and Grand Caravan, Plymouth Voyager and Grand Voyager, and Chrysler Town & Country.

But the No. 3 carmaker is being careful to call the minivan air bag an "air bag system," because technically, it does not meet the letter of the law and must be used in conjunction with three-point seat belts.

Lutz said that while minivan buyers have been clamoring for an air bag and that driver safety is substantially enhanced, it would have taken another 12 to 18 months for Chrysler to redesign the minivan's dashboard and add structural reinforcements to meet Federal Motor Vehicle Safety Standard 208.

There are currently no padded knee bolsters in the minivan. There is also a warning label on the steering wheel saying drivers must wear the seat belt for the air bag to be effective.