May 16 (Reuters) - Warren Buffett's Berkshire Hathaway Inc on Monday revealed a new stake in Apple Inc, in a bet that the stock's price could rebound after iPhone sales fell for the first time.

Berkshire held 9.81 million Apple shares worth $1.07 billion as of March 31, according to a filing with the U.S. Securities and Exchange Commission detailing the company's U.S.-listed stock holdings.

It is not clear who made the investment, Buffett or one of his portfolio managers, Todd Combs and Ted Weschler, who each invest about $9 billion.

Buffett has said he typically makes Berkshire's multibillion-dollar investments, while Combs and Weschler make smaller wagers.

The investment in Apple may have been made with money from the sale of AT&T Inc stock.

Berkshire held $1.6 billion of AT&T at year's end but listed no investment in the phone company in Monday's filing.

Apple shares, which were up 1.4 percent in premarket trading at $91.81, are nearly one-third below their record high last April. They are also well below their price level at the end of March.

The Apple stake deepens Berkshire's commitment to the technology sector, which Buffett has long shunned, apart from a big stake in International Business Machines Corp. He has long said he does not understand the tech sector well enough.

On Monday, Buffett confirmed to CNBC that he offered to help Dan Gilbert, the chairman of Quicken Loans and owner of the Cleveland Cavaliers basketball team, finance a bid to acquire Yahoo Inc.

Reuters first reported Buffett's support on Friday.

Last month, billionaire activist investor Carl Icahn revealed that he had sold his entire stake in Apple, citing the risk of China's influence on the stock.

Apple last month reported its first decline in revenue in 13 years, as growing competition hurt iPhone sales.

(Reporting by Jonathan Stempel in New York; Editing by Lisa Von Ahn and Steve Orlofsky)