Southern California Edison Co. and Ford Motor Co. are expected to announce a partnership today that will include a multimillion-dollar test of plug-in hybrids.

Plug-ins are envisioned as the next-generation development of the current crop of gasoline-electric hybrid vehicles such as the Toyota Prius.

Equipped with more powerful batteries that could be recharged overnight, plug-ins are designed to run for significant periods on electricity alone , greatly increasing their fuel economy.

In addition to saving gas, Ford and Edison said, increased use of plug-in vehicles would lower greenhouse gas emissions and reduce American dependence on imported oil.

The partnership will explore how plug-in hybrids would operate on a day-to-day basis and how they would fit into the state’s electricity grid.

Ford wants to investigate ways to bring down the cost of the vehicles, including by using an innovative technology that allows plug-in vehicles to return unused power to the grid during periods of peak demand.

“They understand the grid, we understand the vehicles and together we can figure out how to optimize the system,” said Susan M. Cischke, Ford’s senior vice president for sustainability, environment and safety engineering.

Under the partnership, Ford will supply a batch of its Escape SUV hybrids to Edison to use. At a later date, it will provide plug-in versions of the vehicle to the utility for testing.

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