LOS ANGELES – The Saturn Aura Green Line, General Motor’s Corp.’s first midsize sedan to go hybrid, will bring a 25% fuel economy boost over the standard base model, the auto maker says.

Saturn unveils the Aura Green Line at the auto show here with plans to price the hybrid-electric vehicle below $23,000, positioning it between the $20,595 XE and $24,595 up-level XR models in the Aura lineup.

Fuel economy for the Aura XE is rated at 20 mpg (11.8 L/100 km) city. A 25% gain would put the Aura Green Line at about 25 mpg (9.4 L/100 km).

The Saturn HEV powertrains are considered “mild hybrids,” in which an internal combustion engine drives the wheels and an electric motor restarts the engine. The engine shuts off when the vehicle is at a complete stop and restarts when the brake pedal is released. Fuel is choked off during deceleration, and regenerative braking captures the vehicle’s kinetic energy to recharge the Aura’s nickel-metal-hydride battery.

The Aura Green Line will go up against full HEV systems in the $25,900 Toyota Camry Hybrid and the venerable $22,175 Toyota Prius, both of which boast better fuel economy.

The Aura’s HEV powertrain is identical to the one in the ’07 Saturn Vue Green Line and continues in the ’08 Vue Green Line, also unveiled today in L.A.

Saturn is marketing the mild HEVs as a way to “drive green without going broke.”

The Green Line’s 2.4L Ecotec VVT 4-cyl. is rated at 164 hp and 159 lb.-ft. (215 Nm) of peak torque. It is mated to a Hydra-Matic 4T45 4-speed transmission.

Production began in October at GM’s Fairfax, KS, assembly plant. Dealerships are to receive the new variant in spring 2007.