Tagliabue said the policy was an effective deterrent. "We don't think the low level of positives indicates a weak program any more than the low level of positives indicates a weak WADA program," he said.

But the commissioner did acknowledge a loophole: The league has no test to detect the use of growth hormone.

"There is a feeling in many quarters it is being abused," said Gary Wadler, a member of WADA, which oversees Olympic drug testing and penalties.

Though there is no urine test for growth hormone, there is an available blood test that was used on several thousand athletes at the Summer Olympics in Athens. But Tagliabue said a U.S. lab has not yet been certified by WADA to conduct such tests.

Wadler also told lawmakers that the world code prohibits more than 40 stimulants but that the NFL bans only eight. "The [NFL] policy tends to omit the stronger stimulants such as amphetamine," Wadler said.

Tagliabue said the league doesn't need to prohibit all of the stimulants because, unlike WADA, it doesn't oversee multiple sports where different drugs may aid performance.

The NFL was also criticized for not disciplining players found to have used steroids at pre-employment events, such as a workout attended by scouts. "I think we should look at that, whether it would be lawful," the commissioner said.

Part of the lawmakers' concern, they said, was based simply by looking at NFL players and noticing the dramatic increase in linemen's size in the past 20 years.

Rep. Stephen F. Lynch, a Massachusetts Democrat, said the number of players weighing more than 300 pounds has soared from fewer than a dozen 20 years ago to between 300 and 400 today.

"Line of scrimmages are bigger than ever," Courson said.

But Tagliabue said the league's heaviest players have high percentages of body fat and don't fit the profiles of steroids users. "They tend to be the antithesis of the sculpted, lean athlete," he said.

From the outset, the committee members adopted a gentler tone with the NFL representatives than they did with Major League Baseball, whose executives were roundly criticized at the March 17 hearing for being lax on steroids.

"The NFL has been different. They've cooperated with the committee from the start," Waxman said.

But Lynch criticized his own committee for not inviting any current players. He called it a "glaring gap."

Last month, the committee subpoenaed a handful of current baseball players, including Orioles Sammy Sosa and Rafael Palmeiro, along with retired sluggers Mark McGwire and Jose Canseco.

This time, Davis suggested the hearing was supposed to be more low-key. "The last time we invited players, we had people saying we were trying to hot-dog it," the chairman said.