CHICAGO – Ben Wallace is crossing Lake Michigan, staying in the same division and bringing his ferocious rebounding and defensive skills to a young team counting on him to be a major force in building a championship contender.

The four-time defensive player of the year, Wallace is leaving the Detroit Pistons and joining the Chicago Bulls, according to a source within the league.

The contract won’t become official until July 12.

Wallace is going from a team that went 64-18 in the regular season to one that was 41-41.

Disappointed with the Pistons’ initial offer to keep him, he agreed to a deal from the Bulls for four years that is reportedly worth $60 million.

“You get a chance to sign the deal of a lifetime. It’s tough to let it go,” Wallace told the Detroit News.

A phone message left Tuesday for Wallace’s agent, Arn Tellem, was not immediately returned.

Wallace will join a team with a young nucleus in Kirk Hinrich, Ben Gordon, Luol Deng, Chris Duhon and Andres Nocioni, one that seriously challenged eventual champion Miami Heat in the first round of the playoffs before losing in six games.

Under coach Scott Skiles, the Bulls have made back-to-back playoff appearances, ending a drought that stretched back to 1998 when Michael Jordan led them to their sixth championship.

After those glory years, the Bulls were never able to lasso the big-name free agent still in his prime. Now general manager John Paxson, who’s been on the job a little more than three years, has done that, thanks to ample salary cap space.

Wallace helped Detroit advance to four straight conference finals – the first team to do so since the Bulls of the early 1990s.

The Pistons won the title two years ago, lost to San Antonio in the championship round in 2005 and were beaten by the Heat in the Eastern Conference finals this season.

At 6-foot-9, Wallace will give the Bulls their best rebounder and defender since another former Piston, one with an even wilder selection of hairstyles and colors, Dennis Rodman.

His talent often overshadowed by his offcourt activities, Rodman was key performer in the Bulls’ final three title runs that featured Jordan and Scottie Pippen.

The Bulls already have scorers, especially on the perimeter. Now they could have a bigger presence in the middle with a 31-year-old center who has gone from undrafted free agent to one of the most aggressive inside players in the NBA.

Reports say the Bulls may now look to trade Tyson Chandler to New Orleans for veteran P.J. Brown or to Atlanta in a sign-and-trade deal for Al Harrington.

At 7-foot-1, Chandler can have big rebounding and shot-block games, but has been foul-prone with an offensive game that is often mechanical.

Wallace ranked fourth in the NBA in rebounding (11.3), ninth in blocks (2.2) and 10th in steals (1.78) during the regular season – the only player among the top 10 in all three categories. He is the fifth player in league history to have 100 blocks and 100 steals in six straight seasons.

Wallace scored 7.3 points a game this past season and has not averaged double digits in any of his 10 years in the league.