NEW YORK, Dec 14 (Reuters) - The report exposing widespread use of steroids in Major League Baseball raised more questions about the depth of the problem in America's pastime and aroused concerns on Friday about the credibility of its evidence.

The Mitchell Report released on Thursday cited the use of steroids and Human Growth Hormone among all 30 major league teams. But some noted the evidence hinged mainly on two sources whose testimony was given in return for plea bargains in federal investigations.

The report, which named more than 80 players as using performance-enhancing drugs in baseball, stirred emotions from the White House to the man on the street. U.S. President George W. Bush, a former part owner of the Texas Rangers baseball team, said the use of steroids in baseball had "sullied" the game.

The biggest splash was the naming of pitching great Roger Clemens, who occupied nine pages of the report. A lawyer for the seven-time winner of the Cy Young Award as his league's best pitcher issued an angry denial on his behalf and said the report slandered his client.

Duke University law professor Paul Haagen described the report as a "peculiar investigation."

"This is wildly under-inclusive," Haagen said, noting "the incredibly limited number of sources" used by former U.S. Sen. George Mitchell, who headed the probe for baseball Commissioner Bud Selig.

Federal probes into the defunct San Francisco-based BALCO lab and an illegal drug distribution ring that snared former New York Mets clubhouse attendant Kirk Radomski and former major league trainer Brian McNamee provided most of Mitchell's material through a plea-deal agreement.

"It seems extraordinarily unlikely that there weren't other networks they didn't get into," Haagen, who teaches sports law, said about the probe that had no subpoena power and struggled with a lack of cooperation from active major league players.

Haagen questioned "the appropriateness of outing even this large a number when you know that there are others."

The report went into great detail about the actions of some players, while others were named with skimpy documentation.

'IS NOTHING SACRED?'

"This probably represents a fraction of the total, actual people that are doing it, that have been doing it," former New York Yankees pitcher Jim Bouton told The Village Voice. "This is not comprehensive by any means."

New York actor Lucas Beck, 25, said the report confirmed the worst fears of fans.

"You hear about one person or another person. And then it's like, whole baseball teams. ... Is nothing sacred?"

Players who, like Clemens, feel wronged, may want to take action but could be reluctant to do so.

"The recourse for players who think they were unfairly named is to bring a defamation action against the investigators or MLB," sports lawyer Brian Socolow of New York firm Loeb & Loeb said.

"Truth is the defense to a defamation claim. My guess is that most players would not want to have to open up their lives in court to an examination of their relationship with Radomski or any of the other distributors of steroids."

Clemens joined home-run king Barry Bonds as the two most celebrated players suspected of using drugs.

Bonds is to stand trial on charges of lying to the grand jury investigating BALCO when he denied using steroids.

Expressing disappointment over Clemens was Republican presidential candidate Sen. John McCain of Arizona, instrumental in turning congressional attention on the problem of steroids in baseball.

"Even in my advanced old age I still have heroes," McCain told ESPN Radio on Friday. "Clemens will go down in history as one of the great pitchers in history and that raises the question, why did he have to do that?"

"We were robbed of an entire era of baseball," wrote Chicago Tribune columnist Rick Morrissey.

"It matters not that it was done at syringe-point instead of gunpoint. We wuz robbed." (Reporting by Larry Fine, Editing by Mark Egan and Peter Cooney)