NEW YORK — Warren Buffett's Berkshire Hathaway this morning said it agreed to buy Burlington Northern Santa Fe in a deal valuing the railroad at $34 billion.

Berkshire Hathaway already owns a stake of about 22 percent in Burlington Northern and said it will pay $100 a share for the rest of the company.

The majority of the stock issued in the deal will be Berkshire's "A" shares, but Berkshire's board also approved a 50-for-1 split of its Class B common stock for holders of smaller amounts of Burlington shares who opt for a share exchange rather than cash. Berkshire's Class B shares closed Monday at $3,265. With the split, each share will be worth $65.30. Burlington shares closed Monday at $76.07. The shares shot up more than 29 percent to $98.25 in premarket trading.

The deal has been approved by the boards of both companies. It would be the biggest acquisition ever for Berkshire Hathaway.

Berkshire also owns MidAmerican Energy Holdings, which controls power companies in the Midwest and Pacific Northwest. The railroad could be a strategic acquisition because its tracks run through both regions, a major coal supply route for power plants.