Carl C. Icahn, the billionaire investor and activist shareholder, has decided to move ahead with plans for a proxy fight at Yahoo and will propose a dissident slate of directors, people with knowledge of the plans said Wednesday.

Mr. Icahn, who has told associates that he has bought as many as 50 million shares of Yahoo, is leaning toward trying to oust the entire board by proposing a slate of 10 candidates, these people said. The deadline for nominating a dissident slate is Thursday.

He is moving ahead with the proxy fight in hopes of pushing Yahoo to restart talks to sell itself to Microsoft. Yet Microsoft has given no indication that it would be willing to restart talks. Mr. Icahn’s decision to try to oust the entire board  as opposed to proposing only a couple of candidates  is considered a high-risk maneuver, analysts said. He might have a better chance of winning a campaign by proposing a smaller slate, several analysts added.

Under the proxy rules, Mr. Icahn can reduce his slate later, but had he nominated a smaller number of candidates he would not be allowed to increase it.