WASHINGTON (AFP) - Henry Waxman, a key US lawmaker in oversight of sport, said on Tuesday that recent court rulings to block bans of two National Football League players weaken advances in fighting banned substance abuse.

Waxman, chairman of the House of Representatives Energy and Commerce Committee, said at a subcommittee hearing on Tuesday that the case involving Minnesota's Pat Williams and Kevin Williams is a disaster in the doping fight.

"These new legal interpretations could render the NFL and Major League Baseball drug testing programs unenforceable, loophole-ridden, and unacceptably weak and ineffective," the Democrat from California said.

"If these rulings prevail, they could wreak havoc with policies designed to curb performance-enhancing drug use in professional sports.

"In fact, if the rulings are taken to their logical conclusion, players on one team could be allowed to use drugs that would subject players on another team to suspensions and fines."

The NFL tried to ban the Vikings defenders four games each after they tested positive last year for the banned diuretic bumetanide, a steroid masking agent.

But the players sued in state court, saying the NFL test policy violated state laws. The case moved to a federal court, which dismissed several claims in May but sent two workplace issues back to a state court, where a judge issued an injunction stopping the NFL from banning the players, a move upheld by a federal appeals court.

A trial is set for March 8, but in the meantime the defenders are able to play.

"We need to find out if the collective bargaining process can solve these problems or whether congressional action is needed," Waxman said.

"One thing is clear: we should not allow the drug policies that the NFL, Major League Baseball, and other sports leagues have put in place to be rendered null and void. That is an invitation to steroid abuse in professional sports and it will inevitably lead to more steroid use on high school fields."

NFL commissioner Roger Goodell was set to seek legislation to prevent union labor deals and their doping rules from being subject to state laws.

US sport league policies essentially leave doping control in the hand of leagues and union leaders to negotiate, a far cry from the doping protections offered under World Anti-Doping Agency (WADA) regulations.