Now Ewan Pritchard wants to turn that soot-spewing school bus into a clean, green plug-in-hybrid machine. High mileage. No more exhaust cloud at each stop.

When Mr. Pritchard, a mechanical engineer, unveiled his plan to a major bus manufacturer in 2002, snickering officials nearly laughed him out of the room. That was before hurricane Katrina hit, and diesel prices skyrocketed.

“When we first talked about this, manufacturers acted as if we were asking them to build flying cars or something,” says Pritchard, hybrid program manager for Advanced Energy, a small nonprofit energy-consulting company in Raleigh, N.C.

That laughter has subsided. Now, the nation’s biggest school-bus maker has orders for 19 buses from districts in 11 states – including Washington, California, Texas, Iowa, Arkansas, and North Carolina.

In Bradenton, Fla., Manatee School District officials last month became proud owners of the nation’s first two plug-in hybrid school buses. Students are catching the spirit of their new ride, too. Emily Mulrine, a district student, helped name her middle school’s new plug-in hybrid bus “Limpio,” the Spanish word for clean.

Such plug-in hybrid buses use both a diesel engine and an electric motor – plugging into a power socket at night to charge batteries. Environmentalists and energy-security hawks love the idea.

“Buses are a great way to use off-the-shelf technology that can reduce pollution and energy use,” says Roland Hwang, senior policy analyst at the Natural Resources Defense Council. “This move creates greater pressure on the automakers to produce similar technology.”

Indeed, while big automakers tout plans to build plug-in hybrid cars a few years from now, Navistar International Corp.’s school bus division, IC Corp., is already rolling out plug-in hybrid buses. This week, another one will be delivered in Pennsylvania.