Putting the integrity of the national pastime under a harsh spotlight, a House committee questioned a panel of superstars Thursday about steroids in baseball, eliciting sharp denials from several -- and in the case of retired home run legend Mark McGwire, an emotion-choked acknowledgment of baseball's doping problems followed by repeated refusal to answer questions about his own possible involvement.

McGwire appeared on a lustrous panel that included his former Oakland Athletic teammate Jose Canseco, Sammy Sosa, Rafael Palmeiro, Curt Schilling and, by video hookup, Frank Thomas -- all of them potential Hall of Famers who were subpoenaed by the Committee on Government Reform.

Canseco, whose recent tell-all book provided some impetus for the hearing, acknowledged his earlier use of steroids, while Sosa, Palmeiro and Thomas all pointedly denied ever having used them.

That focused attention on McGwire, who hit a then-record 70 home runs in 1998 after engaging in a season-long display of mano a mano slugging prowess with Sosa -- a friendly duel that many credited with restoring the nation's love affair with baseball four years after a labor dispute canceled the World Series.

"I'm not here to discuss the past," McGwire said repeatedly when representatives asked about his own possible use of banned substances, as Canseco had alleged in his book, "Juiced." It was the first time he had been asked under oath about steroids, or about his admitted use of the now-banned supplement androstenedione, a steroid "precursor."

His refusal to provide clear responses drew a sharp rejoinder from Rep. Mark E. Souder (R-Ind.), who said: "As far as this being about the past, that's what we do. This is an oversight committee. If the Enron people come in here and say, 'Well, we won't want to talk about the past,' do you think Congress is going to let them get away with that?"

In unsworn comments, McGwire has denied using steroids.

The players' appearance marked a dramatic high point to a long, sometimes digressive, often tense day that began with the testimony of a U.S. senator who also is a Hall of Fame pitcher, and concluded more than 11 hours later with a scolding of baseball Commissioner Bud Selig, players union chief Donald Fehr and other officials.

In calling the hearing, the committee had "decided it was time to break the code of silence that has enveloped the game," said Chairman Thomas M. Davis (R-Va.), citing statistics from the Centers for Disease Control that "more than 500,000 high school students have tried steroids, nearly triple the number just 10 years ago."

Rep. Henry A. Waxman of Los Angeles, the panel's top Democrat, raised the possibility of federal legislation that would impose penalties for use of performance-enhancing drugs for all sports at all levels -- from high school to the pros.

"If we are going to do something for our nation's kids, it seems we are long past the point where we can rely on Major League Baseball to fix the problem," Waxman told the packed hearing room.

Much of the questioning and testimony focused on baseball's steroid testing program, first implemented for the 2003 season, then strengthened in January amid mounting public and political pressure.

The tougher rules came about after the Major League Baseball Players Assn. agreed to reopen its collective bargaining agreement with owners two years before it was set to expire. Though the new policy added penalties for first-time violators and random, year-round tests, it is far weaker than the one used at the Olympics, and was attacked from many quarters on Thursday.

Sen. Jim Bunning (R-Ky.), the hearing's first witness, called it "pretty puny."

Lawmakers complained about a loophole that they said would allow a player to pay a fine of up to $10,000 in lieu of being suspended for a first violation. But baseball officials pledged that players would be suspended -- and publicly named -- the first time they test positive, with penalties increasing on subsequent violations. A fourth positive test carries a one-year suspension, and thereafter the commissioner would determine discipline, including a possible lifetime ban.

Souder called baseball's anti-steroid policy "so full of holes … that if it was cheese, it would definitely be Swiss."

A number of lawmakers said baseball and others sports should adopt the Olympic rule -- a two-year suspension for the first violation and a lifetime ban for the second.

"Baseball will not rest and will continue to be vigilant on the issue of performance-enhancing substances as we move to my stated goal of zero tolerance," Selig said.

Near the end of the lengthy testimony, only 11 committee seats were occupied, the gallery, once standing-room only, was less than half-full and darkness filled the gaps between the shades behind Davis.