Indianapolis Mayor Greg Ballard announced Wednesday morning that the city plans to phase out gasoline and diesel from its vehicle fleet by 2025 in one of the most ambitious steps taken by a major U.S. city to convert to alternative fuels.

Under Ballard's plan, Indianapolis would shift its cars, heavy trucks and even police cruisers to a mix of electricity and natural gas. City buses aren't part of the program.

“The United States' current transportation energy model, driven by oil, exacts an enormous cost financially and in terms of strategic leverage,” Ballard said in announcing the plan.

Ballard said Indianapolis would pursue federal grants that help defray the cost of alternative-fuel infrastructure for its 3,135-vehicle fleet. The Department of Energy helps fund such investments under its Clean Cities Program.

In 2006, the Ballard administration bought 85 hybrid Toyota Camrys for police administrators and detectives.

The new plan calls for the city to replace its current sedans with electric or plug-in hybrids, spokesman Marc Lotter said. After that, the city will work with the private sector to phase in snow plows, fire trucks and other heavy vehicles that run on compressed natural gas. Finally, the city will ask automakers to develop a plug-in hybrid police car, as this doesn't yet exist, Lotter said.

Lotter did not provide an estimate on the cost of the change.

"We are negotiating with the automakers and several international capital fleet firms to get the best deal possible for taxpayers," he said.

The police car switch alone has the potential to save taxpayers $10 million a year in fuel costs, while taxpayers would save $12,000 on each non-police sedan over their 10-year lifespan, Lotter said.

Ballard, a retired Marine officer, hopes that in making the switch, Indianapolis will help the country reduce its dependence on foreign oil.

"This is the mayor's idea," Lotter said. "He views this as a national security issue."

The new vehicles will be purchased on an as-needed basis as older vehicles are retired. Lotter said the city buys about 50 non-police vehicles every year.

City officials and the U.S. Conference of Mayors have researched the issue and found that no other major U.S. city has announced it will convert its entire fleet.

"From everything we know, we are the first city in the nation to take this step," Lotter said.

The city already has charging stations, and is working with private companies to develop more, he said.