NEW YORK – Microsoft Corp. is open to a “major transaction” with Yahoo Inc to either purchase a part or all of the company if a new board of directors is elected, billionaire activist investor Carl Icahn wrote in a letter to shareholders on Monday.

Icahn, a Yahoo shareholder attempting to replace the Internet portal’s board members in at an annual meeting of the company next month, wrote that he has spoken frequently with Microsoft chief executive Ballmer.

Microsoft would be interested in purchasing the whole company or an “alternate” transaction where just Yahoo’s “Search” assets would be purchased, Icahn said.

Ballmer will not enter talks because he fears that Microsoft would be putting its money at risk if it agrees to a transaction and Yahoo mismanages the company during the estimated nine months or more required to get regulatory approval for the deal, Icahn said.

“Steve made it abundantly clear that, due to his experiences with Yahoo! during the past several months, he cannot negotiate any transaction with the current board,” Icahn wrote.

Icahn stated Microsoft would be willing to “immediately” enter into discussions with a new board.

Yahoo shares rose $1.93, or 9 percent to $23.28 in early trading on the Nasdaq Stock Market.

“If Microsoft and Mr. Ballmer really want to purchase Yahoo!, we again invite them to make a proposal immediately,” Yahoo said in a released statement replying to the letter.

“And if Mr. Icahn has an actual plan for Yahoo! beyond hoping that Microsoft might actually consummate a deal which they have repeatedly walked away from, we would be very interested in hearing it,” the company said.

Icahn has proposed a slate of new board members, including himself, that would run Yahoo. If elected he has previously vowed to oust current chief executive Jerry Yang and current board members, whom Icahn accuses of having “botched up” previous negotiations with Microsoft to sell Yahoo.

Microsoft made an offer of $33 per share in a negotiation that ended in May after Yahoo would not sell. Yahoo said Microsoft had not offered enough value to shareholders with the proposal.