Nov. 5 (Bloomberg) -- Warren Buffett’sBerkshire Hathaway Inc. may be downgraded by Fitch Ratings, which said the planned purchase of railroad Burlington Northern Santa Fe Corp. may increase the company’s vulnerability to economic slumps.

Buffett’s expansion into energy and trains is shifting Berkshire toward operations that have “greater sensitivity to general economic conditions than the company’s long-held insurance and holding-company equity-oriented investments,” Fitch said today in a statement. Fitch rates Omaha, Nebraska- based Berkshire “AA+,” its second-highest grade.

Standard & Poor’s, the only one of the three largest ratings firms that still assigns Berkshire its top grade, said yesterday it may cut Buffett’s company because the $26 billion purchase will reduce liquidity at insurance operations. Fitch and Moody’s Investors Service each stripped Berkshire of their top ratings this year as the company posted its first loss since 2001 in the three months ended March 31.

Berkshire will take on $10 billion in net debt as part of the acquisition of the Fort Worth, Texas-based railroad for $100 a share. Buffett, whose firm already owns more than 20 percent of Burlington’s stock, described the deal as an “all-in wager” on the U.S. economy.

“This transaction will decrease the liquidity and capital adequacy of the insurance operations” at Berkshire, S&P said yesterday in a statement.

Swaps Rise

Credit-default swaps used to guard against losses on Berkshire’s debt climbed 1.5 basis points to 164.5 basis points as of 4 p.m. in New York, according to CMA DataVision. The Burlington purchase was announced Nov. 3, and the swaps have climbed 20 basis points since Nov. 2. Berkshire shares slipped $370, or 0.4 percent, to $101,900 at 4:15 p.m. in New York Stock Exchange composite trading.

“An increasing proportion of Berkshire’s assets consist of solid, but comparatively lower credit-quality and less-liquid assets,” Fitch said.

Buffett didn’t return a message left with his assistant Carrie Kizer.

Berkshire bought Marmon Holdings Inc. last year for $4.5 billion, adding more than 100 businesses. Marmon’s Union Tank Car unit manufactures and leases railroad cars. Buffett expanded into the energy industry when he bought utility company MidAmerican Energy Holdings Co. in 1999 and has since bought PacifiCorp and Yorkshire Power.

To contact the reporter on this story: Jamie McGee in New York at jmcgee8@bloomberg.net.

Last Updated: November 5, 2009 16:26 EST