Mercedes-Benz is breaking out of its luxury car mold with the Grand Sport Tourer (GST)-or as the opulently-appointed sport wagon will be called when it goes on sale in 2005, the R-Class.

At its world debut at the Detroit auto show, the car will be billed as the Vision GST-Mercedes' way of saying it is very close to the coming production car. Mercedes says the car, positioned between the E- and S-Class, answers demands for greater versatility and practicality in the luxury car class.

The basic shape and overall proportions remain true to the GST concept car wheeled out in 2002, but other modifications are extensive, including the adoption of conventional front-hinged rear doors in place of the rear-hinged arrangement of the '02 concept. The interior also is less flamboyant and sports a full array of safety features

Mercedes is planning two wheelbases for the GST, with the longer one aimed at the U.S. market that demands three rows of seating and space for six or seven passengers.

The Vision GST is powered by a hybrid drive system combining Mercedes-Benz's 4.0-liter V8 common-rail turbodiesel with an electric motor. Together they deliver 313 hp and 634 lb-ft of torque, though on part throttle the electric motor runs exclusively to reduce fuel consumption by up to 20 percent over diesel engine propulsion.

R-Class will be built at Mercedes' plant in Alabama alongside the second-generation M-Class, with which it will share its engines, seven-speed automatic gearbox, permanent four-wheel drive and air suspension.

While the hybrid is under consideration for eventual sale in the U.S., production versions will first come with a range of V6 and V8 engines-from a base 3.5-liter V6 all the way up to a 6.3-liter V8 in a range-topping RL63 AMG model that's rumored to pack 500 hp. R-Class hits the U.S. market in 2005 as a 2006 model, at prices starting around $50,000. -GREG KABLE and MAC MORRISON