NEW YORK — Announcing the investigation was the easy part for baseball. Now George Mitchell must try to find out how widespread steroid use really was.

In the wake of a searing book about Barry Bonds, commissioner Bud Selig appointed the former Senate Majority Leader — and currently a director of the Boston Red Sox — to lead the investigation.

The probe launched Thursday initially will be limited to events since September 2002, when the sport banned performance-enhancing drugs, but Mitchell has the authority to expand it.

Selig said Mitchell's report will be made public, but didn't set a timetable. By then, Bonds may well have passed Babe Ruth's home-run mark on the way toward Hank Aaron's career record.

"The goal here is to determine facts, not engage in supposition, speculation, rumor or innuendo," Selig said.

Whatever the findings, it will be hard to penalize anyone for conduct before the steroids ban. Baseball began drug testing in 2003 and started testing with penalties the following year.

At San Francisco's home ballpark, Bonds wouldn't discuss the matter.

"I said no, no, no," he said, shaking his head. "I'm going to jump off the Empire State Building — flat on my face," he added, laughing.

Mitchell, meanwhile, said he will not resign from his position with the Red Sox. He also is chairman of The Walt Disney Co., the parent of ESPN, a national broadcast partner of baseball.

"I don't think there's any conflict," he said in a telephone interview with The Associated Press. "I'm going to be independent, have complete independent authority and will act."

ESPN is airing a weekly behind-the-scenes look at Bonds — with the Giants star's cooperation — starting next week.

Along with working for the Red Sox, Mitchell is a former director of the Florida Marlins and served on an economic study committee Selig appointed in 1999. He said he previously announced he would leave the Disney board by the end of the year.

"I've assured the Red Sox owners that should any matter arise, anybody affiliated with the Red Sox will be treated exactly as will anyone else," he said.

John Dowd, the Washington lawyer who headed baseball's investigation of Pete Rose's gambling in 1989, did not like the choice.

"Mitchell doesn't have a great track record with me. It doesn't look like he's independent," Dowd said.

Sen. Jim Bunning, a Kentucky Republican and baseball Hall of Famer, also criticized Mitchell.

"While George Mitchell is certainly a man of great integrity, I believe that baseball would have been wiser to pick someone who is not as close to the game and may be able to take a more objective look into the facts," Bunning said.

Rep. Henry Waxman, a California Democrat who helped lead a congressional hearing last year on steroids in baseball, praised the probe.

"This is precisely what I had asked MLB to do last year," he said. "Finding out the truth about the depth and breadth of this problem is the only way to close the book on this sad chapter of the game's history."

Selig's decision came soon after "Game of Shadows," a book by two San Francisco Chronicle reporters detailing alleged extensive steroid use by Bonds and other baseball stars.

DuPuy said baseball considered Mitchell's potential conflicts of interest.

"Given Sen. Mitchell's integrity, given his background, he was absolutely considered to be the perfect choice for this job," he said.

New York Yankees first baseman Jason Giambi, who like Bonds testified before a federal grand jury in 2003, said he'd have "no problems" with an inquiry. Giambi reportedly admitted to the grand jury that he had used steroids.

"I did the things I needed to do, took care of it and played last year and have just gone forward. I'm not really worried about it," he said.

Teammate Gary Sheffield also testified and said of his cooperation: "If I have to, I will. I'm going to do whatever the law expects me to do, but other than that it's a waste of my time."