NEW YORK (Reuters) - Noted investors including mutual fund giant Fidelity Investments and hedge fund manager Leon Cooperman bought shares of JPMorgan Chase & Co in the first quarter, just before the stock was rocked by revelations of a surprise $2 billion trading loss.

Shares of the largest U.S. bank by assets have fallen 20 percent since the end of the first quarter, including 10 percent in the three days since the bank disclosed on May 10 the huge trading loss. Chief Executive Jamie Dimon, speaking at the bank's annual meeting on Tuesday, said he was implementing "many changes in policies and procedures" to avoid future surprises.

Even after the trading misstep and the stock's decline, the first-quarter bets on JPMorgan could still pay off. Many investors see the stock as deeply undervalued.

"Two billion dollars may have a noticeable impact on my financial statement and yours, but it is nearly a rounding error for JPMorgan," said Nicholas Tompras, a manager at ACR Alpine Capital Research in St Louis, which owns shares of JPMorgan.

The trading loss should be viewed in light of the bank's $2.2 trillion of tangible assets, $130 billion in tangible capital and $18 billion of annual earning power, Tompras said.

Boston-based Fidelity, one of the largest managers of U.S. mutual funds, increased its holdings of JPMorgan to almost 141 million shares at the end of the first quarter, an 11 percent increase from the end of 2011, according to a securities filing on Tuesday. The filing combines holdings at Fidelity's hundreds of funds with other units such as Pyramis Global Advisors LLC, which manages money for large institutions.

Fidelity declined to comment.

Cooperman more than doubled his stake in JPMorgan during the first quarter, to 2.2 million shares. The New York-based manager was not immediately available for comment.

Fellow hedge fund manager David Tepper, who has successfully traded in and out of major bank stocks several times since the financial crisis, was a buyer not of JPMorgan but of two other financial giants in the first quarter. Tepper's Appaloosa Management LP added 7.5 million shares of Bank of America Corp and 6.1 million shares of Citigroup Inc. Shares of both banks have declined more than 20 percent since the end of the quarter.

Tepper declined to comment.

All of the purchases were disclosed in required quarterly filings with the Securities and Exchange Commission. The firms may have sold shares since the end of the quarter or hedged using positions that were not disclosed.

(Reporting By Aaron Pressman with additional reporting by Ross Kerber in Boston; editing by John Wallace)