Warren Buffett, the world¿s second-richest man, says he will give the bulk of his fortune, which is currently valued at about $44 billion, to the Bill and Melinda Gates Foundation.

The 75-year-old chairman of

Berkshire Hathaway

said he would begin making annual stock donations next month to the fund established by the billionaire founder of

Microsoft

, as well as to four other foundations.

The philanthropic plan, outlined in

letters Buffett posted on Berkshire Hathaway¿s Web site, marks a dramatic shift from his previously stated goal of giving his fortune away only after death. He also previously intended to give the bulk of it to the Susan Thompson Buffett Foundation, established by him and his late wife, Susan.

Buffett said he has earmarked 10 million Class-B Berkshire shares for the Gates Foundation. At Friday's closing level, those shares are worth $30.71 billion, a sum that will greatly boost the capabilities of the Gates Foundation, which is already the world's largest philanthropy with about $30 billion in assets. Set up in 1995, the foundation is run by Gates' wife, Melinda. The richest man in the world, Gates sits on the Berkshire-Hathaway board.

Buffett also has set aside 1 million Class-B shares for the Susan Thompson Buffett Foundation and 350,000 Class-B shares each to the Howard G. Buffett, Susan A. Buffett and NoVo (Peter A. Buffett) Foundations. The latter three are headed by Warren Buffett's children.

The Berkshire-Hathaway chairman currently holds only Class-A shares of his company's stock, which closed Friday at $92,100. But in his letters to the foundations, Buffett said he would soon convert "a number" of his shares to Class-B stock.

Buffett's decision was first reported in an

article on

Fortune

magazine's Web site written by editor-at-large Carol Loomis, who is a longtime friend of Buffett's.