UPDATE 3-Warren Buffett buying railroad Burlington Northern

* Deal is Buffett's biggest ever

* Buffett calls it a bet on the U.S. economy

* Price of $100/share is a premium of 31.5 percent

* Deal values railroad at $34 billion

* Buffett already owns 22.6 pct of railroad's shares (Adds further Buffett quotes, Berkshire stock split, deal details, comment, byline)

By Nick Zieminski

NEW YORK, Nov 3 (Reuters) - Warren Buffett's Berkshire Hathaway Inc (BRKa.N) (BRKb.N) will pay $26 billion to buy out railroad Burlington Northern Santa Fe Corp (BNI.N) in what the billionaire investor called a bet on the U.S. economy.

The deal, Buffett's biggest-ever acquisition, is priced at a premium of 31.5 percent over BNSF's closing stock price on Monday and values the railroad at $34 billion.

"It's an all-in wager on the economic future of the United States," Buffett said in a statement, adding that railroads are key to the U.S. economy and will benefit as recovery takes hold. "I love these bets."

Berkshire Hathaway will pay $100 per share in cash and stock for the 77.4 percent of BNSF shares it does not already own. Berkshire will also assume $10 billion of BNSF debt. The deal is expected to close in the first quarter of 2010.

Shares of railroad companies rallied in premarket trading following news of the deal, and stock index futures pared losses.

"For the market, it can be seen as a sign of confidence (about the economy)," said Peter Boockvar, equity strategist at Miller Tabak + Co in New York, adding it was logical for Buffett to buy the rest of the railroad.

"Berkshire is seeing way past some impending economic recovery signs now and looking into the future," he said.

BNSF shares were up 29 percent to $98.18 in premarket trading.

Berkshire's board approved a 50-for-1 split of the company's Class B common stock to help ease the way for the deal.