PHOENIX – Former Senate Majority Leader George Mitchell warned baseball owners that a lack of cooperation with his investigation into steroid use will “significantly increase” the chances of government involvement.

Speaking to owners at baseball’s quarterly meetings, Mitchell said he intends to interview active players and raised the possibility that Congress or other government authorities could compel testimony.

“I believe it will be in your best interests, and the best interests of baseball, if I can report that I have received full cooperation from your organizations, and from others, in conducting this investigation,” Mitchell said in remarks that were released to reporters.

Mitchell cited last week’s Hall of Fame vote to underscore the importance of his investigation. Mark McGwire was picked on 23.5 percent of ballots – far below the necessary 75 percent needed for induction. The vote was viewed by many as the first referendum on how history will judge an age when bulked-up players came under suspicion of using performance-enhancing drugs. Baseball didn’t ban steroids until after the 2002 season.

“If nothing else, the results of the Hall of Fame voting last week, and the reaction to it, offer fresh evidence that this issue will not just fade away,” Mitchell said. “Whether you think it fair or not, whether you think it justified or not, Major League Baseball has a cloud over its head, and that cloud will not just go away.”

Mitchell cannot compel testimony. He warned the clubs that Congress or other federal or state authorities that do have subpoena power could get involved.

“I believe that a report that is not credible and thorough will significantly increase the possibility of action by others, especially if it’s the result of a lack of cooperation by the clubs or by anyone else who is or has been involved with baseball,” Mitchell said.

The House Oversight and Government Reform Committee held a series of hearings on steroids and pro sports in 2005 and 2006.

“The use of steroids in professional sports continues to be an issue the committee is interested in, and we are looking forward to learning more about the progress Senator Mitchell has made in his investigation,” said Rep. Henry A. Waxman, the California Democrat who chairs the committee.

Keith Ausbrook, Republican general counsel for the committee, said he’s almost certain Mitchell has not been in contact with the panel recently about this issue.

“We’ve certainly been very interested in his investigation and what the results are going to be,” Ausbrook said. “If he’s not getting anywhere, we’ll certainly consider whether to re-engage in it.”

The Players’ Association declined comment, spokesman Greg Bouris said.

Mitchell did not speak to reporters after addressing owners. He was hired by commissioner Bud Selig last March following more than a year of allegations against Barry Bonds, McGwire and other stars. No timetable was set for Mitchell’s report.

Bonds is under investigation by a federal grand jury as to whether he perjured himself when he testified in 2003 in the BALCO steroid-distribution case that he hadn’t knowingly taken any performance-enhancing drugs.

The San Francisco Giants are negotiating a contract with Bonds, who needs 22 home runs to surpass Hank Aaron’s mark of 755. Speaking to reporters at a golf tournament in the Dominican Republic this week, Bonds declined to discuss ongoing negotiations with the Giants or his reported positive test for amphetamines last year.