CHICAGO -- Tribune Co. said it plans to sell the Chicago Cubs at the end of the 2007 baseball season, putting one of its most valuable assets on the block as it simultaneously announced Monday that real estate magnate Sam Zell was acquiring the media conglomerate.

Analysts have estimated that the Cubs could fetch $600 million or more. Tribune bought the team in 1981 for $20.5 million.

Prominent names mentioned as possible buyers of Chicago's "Lovable Losers":

• Jerry Colangelo, former D-Backs, Suns owner

• Mark Cuban, Dallas Mavericks owner

• George Will, national columnist

• Bill Murray, actor

• Don Levin, Chicago Wolves owner (minor-league hockey)

"The Cubs have been an important part of Tribune for more than 25 years and are one of the most storied franchises in all of sports," said Dennis FitzSimons, Tribune chairman, president and chief executive officer. "In our last season of ownership, the team has one mission, and that is to win for our great fans."

Tribune said the company's 25 percent interest in Comcast SportsNetChicago would be part of the sale package.

The Cubs' strength as a sports franchise -- and the lure of potentially steering them to their first championship since 1908 -- has attracted the interest of many potential buyers. Billionaire entrepreneur Mark Cuban, actor Bill Murray and columnist George Will are among those rumored to have interest, along with numerous Chicago business figures.

Jerry Colangelo, chairman of the NBA's Phoenix Suns and former owner of both the Suns and baseball's Arizona Diamondbacks, told The Associated Press in November that he would have "great interest" in buying his hometown baseball franchise if it became available and had already held preliminary discussions with others who might join him in a bid.

Speculation that the struggling Tribune Co. might sell the Cubs ramped up last fall when it put itself up for possible sale, under pressure from disgruntled shareholders. It intensified with the club's offseason spending spree, including signing outfielder Alfonso Soriano to an eight-year contract for $136 million -- the fifth-richest contract in major league history.

Tribune had said for months that it would focus first on a sale of the entire company before considering selling individual pieces, which also include 23 television stations and 11 newspapers, including the Chicago Tribune, Los Angeles Times, Newsday and eight other dailies.

The Tribune Co. bought the Cubs for $20.5 million in 1981. Some analysts have estimated the franchise could fetch a $600 million sale price.

That sale was announced Monday morning when it said it had agreed to a complex deal in which Tribune will go private and billionaire Zell will invest $315 million in the deal.

Cubs President John McDonough said the mission has not changed for the team.

"The goal is to win a World Series for our great fans," he said. "Under the leadership of Lou Piniella, we are on track and believe 2007 will be a very successful season."

The fact the ownership change will not occur until after the season will help maintain the focus on day-to-day operations, he said.

While the Cubs are renowned for their losing ways, they also have become more of a box-office success under Tribune's ownership and have spent dramatically more money in recent years, as McDonough noted.

Others who expressed interest in buying the Cubs recently include Chicago businessman Don Levin, owner of the Chicago Wolves minor-league hockey team, and a prospective ownership group of 15 investors that includes Tom Begel, chairman of Chicago-based TMB Industries.