DETROIT -- Ford Motor Co. is developing a 4.4-liter V-8 diesel engine for use in the F-150 pickup later this decade.

The new diesel engine awaits final approval, but suppliers and industry sources say Ford is well along in the planning process. The engine would be a scaled-up version of a 3.6-liter V-8 diesel Ford began producing for Range Rovers in April at a plant in Dagenham, England.

Timing of the new diesel's appearance in the F-150 isn't certain. If the 4.4-liter engine is approved, sources say Ford would need at least two or three years to launch production.

Company spokesman Nick Twork declined to confirm Ford's plans for the 4.4-liter engine. "The best thing to say is we intend to maintain truck leadership," Twork said. "We have some great diesel engines in our lineup."

Diesel engines are available in a variety of larger pickups from Ford and other automakers. Now several companies are believed to be considering diesels for use in half-ton pickups.

For several years, Ford has considered proposals for a diesel F-150 pickup. The company had considered buying the engine from an outside supplier. Now Ford wants to produce its own engine.

Sources say Ford could produce the 4.4-liter engine in Dagenham and ship it to the United States. Although Ford has not settled on the engine's production volume, suppliers and analysts say Ford could produce 100,000 diesel-powered F-150s. Ford sold 901,463 F-series trucks in 2005.

Sources said the engine also could be used in Ford's Expedition SUV