Billionaire investor Carl Icahn threatened to seek control of Yahoo! Inc.'s board if the Internet company doesn't revive takeover talks with Microsoft Corp. over its failed $47.5 billion bid.

Icahn said today that he owns the equivalent of 59 million Yahoo shares, and has permission to acquire up to $2.5 billion worth. He created a slate of 10 nominees for board seats, including Mark Cuban and Frank Biondi Jr. All 10 of Yahoo's directors are up for re-election at the annual meeting on July 3.

Icahn has led proxy fights at companies such as Motorola Inc. and drugmaker ImClone Systems Inc., frequently pushing them to sell part or all of their businesses to help revive sagging share prices. Today he urged Yahoo to make a deal with Microsoft, saying the combination "is by far the most sensible path" if they want to take on Google Inc.

"The board of directors of Yahoo has acted irrationally and lost the faith of shareholders and Microsoft," Icahn, 72, said in a letter to Yahoo's board. "I sincerely hope you heed the wishes of your shareholders and move expeditiously to negotiate a merger with Microsoft, thereby making a proxy fight unnecessary."

Yahoo, based in Sunnyvale, California, climbed 39 cents, or 1.4 percent, to $27.53 at 10:11 a.m. New York time in Nasdaq Stock Market trading. The stock had fallen 32 percent in the year before Microsoft's bid. Microsoft, the world's biggest software maker, gained 3 cents to $29.96.

Yang's Snub

Yahoo Chief Executive Officer Jerry Yang rejected Microsoft's $33-a-share offer this month, saying his company was worth at least $4 more. Buying Yahoo would have helped Microsoft compete with Google in Internet searches and online advertising, a market the company expects to almost double to about $80 billion by 2010.

Google, based in Mountain View, California, handled almost two-thirds of U.S. search queries in March. That compared with 21.3 percent for Yahoo and less than 10 percent for Microsoft, according to ComScore Inc., a market researcher in Reston, Virginia.

Accepting Microsoft's offer is a better option than going it alone, Icahn said in the letter. The board "completely botched" negotiations with Microsoft, prompting its shareholders to ask Icahn to step in, he said.

Icahn is acting as a "surrogate" for Microsoft by waging a battle for board seats that may convince Yahoo to sell to the software maker, Troy Mastin, an analyst at William Blair & Co. in Chicago, said in an interview with Bloomberg Television.

Smart Play

"I think he's playing his cards pretty smart here," said Mastin, who expects Yahoo shares to perform in line with the broader market. "I wouldn't be surprised to see Microsoft and Yahoo together in the next few months."

Icahn and Adam Miller, a spokesman for Yahoo, didn't immediately return phone messages. Microsoft spokesman Frank Shaw declined to comment.

Microsoft had created its own slate of potential directors for Yahoo as CEO Steve Ballmer weighed a hostile takeover. After Microsoft walked away from the deal, its law firm sent letters to the 10 potential board members and some alternates releasing them from their contracts, a person familiar with the matter said.

"For Microsoft to get involved in a proxy fight, it would have created a lot of ill will with Yahoo shareholders," said Youssef Squali, a Jefferies & Co. analyst in New York. Bringing Microsoft in later as a white knight "may turn out to be the winning strategy."

Icahn's Options

Should Microsoft fail to reemerge as a bidder, Icahn may have to find other ways to boost shareholder value, such as aligning the company with Google or selling stakes in Yahoo's Asian operations, said Ross Sandler, an RBC Capital Markets analyst in New York.

"It opens up the door for everything from completely carving this thing apart and extracting value that way, to getting Microsoft back on board, to getting a new management team there to run it," Sandler said. He advises investors to buy Yahoo shares, which he doesn't own.

Icahn's board nominees include three executives with experience in the entertainment business. Cuban, owner of the Dallas Mavericks professional basketball team, co-founded Broadcast.com Inc. and sold it to Yahoo for $4.7 billion in 1999. He also co-founded HDNet, the high-definition cable TV network.

Biondi is the former chief executive officer of Viacom Inc. and Universal Studios Inc. Another nominee, Robert Shaye, is co- CEO of New Line Cinema.

Nominees

Icahn also nominated himself and Keith Meister, principal executive officer of Icahn Enterprises Inc. The rest of the slate includes Lucian Bebchuk, a professor at Harvard Law School; John Chapple, the former CEO of Nextel Partners Inc.; Adam Dell, managing general partner of Impact Venture Partners; Edward Meyer, CEO of Ocean Road Advisors Inc.; and Brian Posner, former CEO of ClearBridge Advisors LLC.

Icahn built his reputation in the 1980s as a corporate raider, targeting big companies such as Phillips Petroleum Co., Texaco Inc. and Trans World Airlines Inc.

At Motorola, Icahn backed the idea of splitting off the company's mobile-phone business, a plan CEO Greg Brown adopted in March. Icahn also has supported an effort by video-store chain Blockbuster Inc. to purchase electronics retailer Circuit City Stores Inc. He said last week that he would buy the company himself if Blockbuster couldn't get financing.

Icahn also prodded BEA Systems Inc. to accept a takeover offer from Oracle Corp. Icahn took some credit for the $8.5 billion transaction, telling Bloomberg in January that he helped convince BEA's board to agree to terms.

"He's proven to be as successful in these situations as any activist investor—probably ever," RBC's Sandler said.