SAN FRANCISCO — Yahoo Inc. chief executive Jerry Yang spent months fending off Microsoft Corp.'s unsolicited takeover bid. Now he may only have a few weeks to persuade the software maker to revive its last offer of $47.5 billion, or risk being fired in a shareholder mutiny led by activist investor Carl Icahn.

Spurred on by outraged shareholders, Icahn notified Yahoo yesterday that he will lead a revolt to oust Yang and the rest of the Internet company's board unless they renew the negotiations with Microsoft that fell apart May 3 when the two sides couldn't agree on a price.

In a response late yesterday, Yahoo's chairman, Roy Bostock, signaled that the Sunnyvale-based company's board is prepared to battle the New York financier.

Icahn has nominated an alternate slate of directors to replace the current board in a July 3 election at Yahoo's annual meeting.

If the maneuver is successful, an Icahn-led board presumably would fire Yang as CEO and try to negotiate a sale to Microsoft.

In his letter to Bostock, Icahn lambasted the board's actions as "irresponsible" and "unconscionable," given that Yahoo's stock stood at $19.18 before Microsoft first made its bid. He urged the board to reopen the talks.

As leverage in the battle, Icahn revealed, he has spent more than $1 billion snapping up 59 million Yahoo shares and options to give him a 4.3 percent stake in the company.

He plans to seek approval from the Federal Trade Commission to acquire up to $2.5 billion in Yahoo stock, including his current holdings.