WASHINGTON  The Obama administration’s 2012 budget proposal will include a request for money to help develop small “modular” reactors that would be owned by a utility and would supply electricity to a government lab, people involved in the effort say.

The department is hoping for $500 million over five years, half of the estimated cost to complete two designs and secure the Nuclear Regulatory Commission’s approval. The reactors would be built almost entirely in a factory and trucked to a site like modular homes.

In promoting the reactor, the administration’s immediate goal is to help the Energy Department meet a federal target for reducing its carbon dioxide emissions by relying more on clean energy and less on gas and coal. Like other federal agencies, the department is required by an executive order to reduce its carbon footprint by 28 percent by 2020.

Yet the longer-term goal is to foster assembly-line production of the small reactors at a far lower cost than construction of conventional reactors. The reactors could even replace old coal-fired power plants that are threatened by new federal emissions rules and sit on sites that already have grid connections and cooling water.