WASHINGTON—When Major League Baseball announced a new drug-testing policy two months ago, the supposed get-tough approach was hailed on Capitol Hill.

But on the eve of testimony before a House committee from some of the sport’s biggest stars, members of Congress criticized the plan after getting a chance to read the fine print.

Sen. John McCain, who in January said the agreement “appears to be a significant breakthrough,” changed course Wednesday.

“I can reach no conclusion, but that the league and the players union have misrepresented to me and to the American public the substance of MLB’s new steroid policy,” the Arizona Republican wrote to baseball commissioner Bud Selig and union head Donald Fehr.

Saying he expects changes to the policy, McCain added: “To do anything less than that would constitute a violation of the public’s trust, a blow to the integrity of Major League Baseball, and an invitation to further scrutiny of the league’s steroid policy.”

Echoing McCain’s sentiments were Reps. Tom Davis, Henry Waxman and Cliff Stearns. Davis, R-Va., is the chairman and Waxman, D-Calif., is the ranking minority member of the Government Reform Committee. That panel was to hear Thursday from six subpoenaed players and commissioner Bud Selig, along with other baseball executives, medical experts, and the parents of two amateur athletes who committed suicide after taking steroids.

Sen. Joseph Biden said Thursday on ABC’s “Good Morning America” that he thinks baseball owes an explanation. “This is about who we are as a nation,” the Delaware Democrat said. “It makes a mockery of sport.”

Without immunity from prosecution, some players were thought to be considering invoking their Fifth Amendment right to refuse to answer questions.

Current or former players Mark McGwire, Sammy Sosa, Jose Canseco, Rafael Palmeiro and Curt Schilling were to appear, while two-time AL MVP Frank Thomas was given permission to testify via video connection.

That group includes three of the top 10 home run hitters in major league history: McGwire ranks sixth with 583, Sosa is seventh, Palmeiro 10th. And McGwire and Sosa were widely credited with boosting baseball’s popularity in 1998 when they engaged in a head-to-head chase to break Roger Maris’ season record of 61 homers. McGwire finished with 70, Sosa with 66.

One subpoenaed player was excused from testifying at all: New York Yankees slugger Jason Giambi, who reportedly told a grand jury investigating a steroid-distribution ring in 2003 that he used steroids.

Never invited to appear was another star who testified to that grand jury: Barry Bonds, who broke McGwire’s season record by hitting 73 homers in 2001 and is approaching Hank Aaron’s career mark of 755.

Selig was to appear, along with baseball executive vice presidents Rob Manfred and Sandy Alderson, Padres general manager Kevin Towers and union head Donald Fehr.

The hearing was called over baseball’s steroid-testing plan, agreed to by owners and players this year under pressure from Congress but still unsigned.

Punishments that congressmen already had called too weak were criticized further Wednesday when the committee released the draft testing agreement and pointed out that it retains a provision that allows the commissioner to substitute fines for suspensions. A player could be docked $10,000 instead of receiving a 10-day ban for a first offense, for example.

Manfred responded that players would be suspended in all instances for positive tests.

Davis and Waxman wrote to Selig and Fehr on Wednesday expressing concern.

“Even if players are suspended, the public disclosure is limited to the fact of their suspension with no official confirmation that the player tested positive for steroids,” they said. “In contrast, the Olympic policy calls for a two-year suspension for a first offense.”

They also said the deal didn’t prohibit four steroids banned by the World Anti-Doping Agency, calling it a “significant omission.” “

Canseco, who retired in 2001 with 462 homers, asked for immunity so he could testify fully, but that request was turned down Wednesday. It was Canseco’s recent best-selling book that brought a lot of attention to the issue; he wrote that he used steroids and that he injected McGwire with them. McGwire has denied using performance-enhancing substances.

The committee started by inviting witnesses _ with no luck. So the panel issued subpoenas, compelling them to show up. Major League Baseball said it would fight the subpoenas; Davis and Waxman responded by threatening contempt of Congress charges.

The lawmakers have said they viewed the hearing as a chance to find out about the role of steroids in the majors and to address the effect on young athletes _ not to expose whether individual players used the drugs.

“With all the reports we’ve had in the past decade _ Major League Baseball has refused to investigate,” Waxman said last week. “Now with the great interest in the subject because of Jose Canseco’s book, and people who said they did and did not use steroids, it’s brought things to a head.

“Major League Baseball is taking an attitude that they don’t want to know what happened or maybe they did know and they don’t want anyone else to know.”

Some players around spring training said Wednesday they had no interest in watching the hearings; others, like Royals first baseman Ken Harvey, planned to follow news coverage.

“I want to see what questions they’re going to ask,” Harvey said. “They keep saying it’s not a witch hunt, but I think it might be.”

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AP Sports Writer Steve Brisendine in Surprise, Ariz., contributed to this report.