Shell, the Dutch oil giant, is expected to finish work in September on a plant it is building at the city garage that will extract hydrogen from water, producing what would be the equivalent of up to about 40 gallons of gas a day. Also next month, the city will receive the five General Motors vehicles at a cost of $705,000, all funded by grants from Shell and two state authorities that promote alternative fuels.

The three cars and one of the pickups will run on 100 percent hydrogen, and the second pickup will pioneer another nascent technology by running on a blend of hydrogen and natural gas that also will be produced at the city garage.

Public Works Commissioner Joseph "Bud" Nicoletti, who is overseeing the hydrogen program for the city, said White Plains has become "old hat" at using "cutting edge" energy technology.

"We've been doing this for quite a few years," Nicoletti said about using the alternative-fuel vehicles, which began when the city was the first municipality in the state to pump ethanol into city vehicles in 1978. Today, White Plains fuels a dozen vehicles, including a street sweeper, on compressed natural gas under a program that made it the first city in New York to win a federal Clean City award.

The hydrogen fueling station that opens on Kensico Avenue next month will join a handful that Shell is developing nationwide, including one in Washington and another in Los Angeles that already are operating. Several other hydrogen stations are planned in the New York City and Los Angeles areas, but Shell gave up on opening a station on Central Avenue in Greenburgh because the site was too small to hold the equipment needed to store hydrogen at a high pressure, said Tim O'Leary, a spokesman for Shell Hydrogen in Houston.

O'Leary said hydrogen vehicles still are at least a decade away from large-scale commercial production because of their huge cost - each has a $100,000-plus price tag - and because there are so few stations where they can fill up.

"We see ever-increasing numbers of fuel-cell vehicles each year," O'Leary said. "But as far as commercialization, mass production, car manufacturers say that's not going to be for quite some time, the middle of the next decade and out."

Hydrogen fuel-cell vehicles run on batteries, while the vehicles coming to White Plains will use internal combustion engines to burn hydrogen. Fuel-cell vehicles produce no emissions, while the internal combustion vehicles emit only water vapor.

In an interview last year when White Plains and Shell announced the partnership that would bring the hydrogen vehicles to the city, O'Leary said Shell chose the city because it is in a metropolitan area with demographics that suggest residents would be open to the technology and could afford it.

A relatively high percentage of residents in the region already drive hybrid cars, which run on batteries and gasoline, such as Toyota's Prius, O'Leary said.