Warren Buffett’s Omaha-based Berkshire Hathaway Inc. agreed to buy the NRG NV reinsurance unit of ING Groep NV for about $441 million, its second acquisition this week, Reuters reported.

ING said today it is selling its Dutch reinsurance unit to an insurance unit of Berkshire so it can focus on its own insurance, banking and asset management businesses. ING expects the sale to result in a $147 million after-tax loss in 2007 and an increase of 0.47 percentage points in its debt-to-equity ratio in 2008.

ING plans to use sale proceeds to fund operations, previously announced acquisitions and a 5-billion-euro share buyback program, an ING spokesman said. The NRG transaction is subject to regulatory approval and is expected to close in the first half of 2008, ING said.

On Tuesday, Berkshire agreed to pay Chicago’s Pritzker family $4.5 billion for 60 percent of Marmon Holdings Inc, whose products include railroad tank cars, pipes, wiring and water treatment systems. Berkshire plans to buy the rest of Marmon by 2014.

The Wall Street Journal reported today that Buffett is set to launch a bond insurer targeting local governments, seeking to profit from troubled credit markets. The new enterprise, Hathaway Assurance Corp., is set to start operating today in New York state and guarantee the bonds that cities, counties and states use to finance public works, the report said, quoting Buffett from an interview.