Imagine the surprise of seeing he new Toyota Prius sitting in the neighborhood garage with a yellow industrial-strength power cord coming out of hybrid car's back end and snaking around to a 120-volt electrical outlet. This is the New Plug In Hybrid. This could be the future of Hybrid cars in general

The future, if Toyota and a few other car makers have anything to say about it, will see a lot more of these cars. Technological hurdles on the cost and efficiency of hybrid-car batteries will have to be overcome, but in the past couple of weeks, two major developments seemed to encourage the possibility that these cars may actually get built and sold to the public.

The Natural Resources Defense Council and the Electric Power Research Institute, an electrical power industry group, said widespread use of plug-in Hybrids, which use little gasoline, would help the environment and reduce oil consumption.

Hybrids at UC

Less than a week later, Toyota said it would provide two factory-made Prius plug-in Hybrids to the University of California - at campuses in Berkeley and Irvine - for a two-year test on U.S. roads.

The Chronicle's own test drive the other day showed that the plug-in Prius is much like the regular plugless one sold in Toyota showrooms, but with a few tantalizing exceptions. By far, the most arresting (or non-arresting) detail is when you start out driving the plug-in. The car is absolutely silent - that's the electric motor - but when you move down the street, it continues its silence (the regular Prius turns on its engine soon after takeoff).

By now, however, you're not caring about electric-this, gasoline-that. You are mesmerized by a dashboard-mounted instrument whose digital readout shows your gas mileage leaping from 54 mpg to 145 mpg to 421 mpg to 999 mpg, depending on how much of a lead foot you are.

Normal hybrid cars - if such a vehicle can be called normal - get down the road using a combination of electric motor and gasoline engine. In the Prius, the nation's most popular hybrid, the electric motor is powered by nickel metal hydride batteries. That car gets an average of 46 mpg, according to the Environmental Protection Agency.

In the plug-in hybrid owned by Felix Kramer, here in Redwood City, those original batteries have been replaced by some 4,000 lithium-ion batteries, which are twice as powerful as the old batteries.

Kramer's car is the showpiece of his homegrown plug-in hybrid organization, the California Cars Initiative, a 5-year-old nonprofit that extols the virtues of plug-ins - the car is emblazoned with decals touting its 100-mpg-plus capabilities.

The car, a 2004 model, was converted by Energy CS, in Monrovia (Los Angeles County) at a cost of about $15,000. Energy CS is one of a handful of firms in the United States and Canada converting Priuses in to plug-in Hybrids.

Kramer loves to open the car's hatchback and show visitors the bright red board covering the batteries. Glued to the board are photos of Kramer at various enviro events - here with Bill Clinton, there with Al Gore.

Kramer is evangelical in his bid to get people to know about these cars, and he has become well known through his public appearances and his Web site.

While we were tootling along Alameda de las Pulgas, Kramer's cell phone rang. He picked up, listened and then said politely that to get a full answer to the question, the caller should consult Kramer's Web site ( www.calcars.org ).

"How do I get one?"

"Most of the phone calls are, 'How do I get a plug-in hybrid?' " Kramer said. "The calls used to be, 'What is it?' Now they're, 'How do I get one?' or 'Why aren't the automakers making one?' "

In downtown Redwood City, the car, with its 100 mpg decals, gets noticed.

A man who gave his first name as Blake (no last name, please) said of the Prius, "I think they're great if you drive a lot. I pretty much ride a bicycle, walk, take Caltrain."

Blake's companion, Jim Zaccanti, from Darby, Mont., when asked whether he would buy one of these cars, said, "It's not worth it. I could buy 20 years' worth of gas for that."

Back at Kramer's house, he took a look at the "control displacement unit" on the dashboard to determine the car's overall mileage during our outing.

"A bit over 122 miles per gallon," he said with a smile. Then he got out of the car and plugged it back into the wall.