Four months after signing undergraduate Herschel Walker to the richest contract in professional football history, Commissioner Chet Simmons told the Senate Judiciary Committee yesterday that his U.S. Football League has imposed a moratorium on signing college undergraduates while looking for a suitable way to make exceptions for the rare athlete.

The committee is considering a bill proposed by Sen. Arlen Specter (R-Pa.), that would protect professional football from antitrust lawsuits filed by any college player who protests the existing eligibility rules.

"Although we agree with the concept of (the bill), we believe that more flexible eligibility rules may preclude the need for congressional action," Simmons said. "There are thoughtful modifications that can be made in the existing eligibility rules . . . that can address better the rights of young men . . . The athlete should have a say. There are areas which we must examine, like the 24-year-old player, the player with scholastic ineligibility . . . "

Pete Rozelle, commissioner of the National Football League, was asked by Specter what the NFL would do if the USFL decided to raid the college campuses and sign the best players for the next three or four years. Rozelle said the NFL would attempt to stand by its 50-year policy of not signing undergraduates.

"We don't think the players would be physically and mentally prepared," said Rozelle, "and we'd like to have a good relationship with the colleges."

Dick Dull, Maryland athletic director who also testified before the committee and is in full support of the bill, said Rozelle's position was "not realistic. If one (the USFL) goes and causes an exodus of undergraduates into the professional ranks, the NFL would have to abandon the policy, due to economic survival."

Dull said such an exodus is a "very real possibility."

But Simmons testified that the league has imposed its moratorium, "until we are able to deal with the appropriate collegiate bodies to deal with specific sets of circumstances."

Simmons put forth Walker, the Heisman Trophy winning running back from Georgia, as such an example. "I don't think any expert could have testified that this young man wasn't emotionally, physically and creatively ready to play professional football," Simmons said.

Simmons also testified that the USFL signed Walker because it feared a lawsuit. Specter reminded Simmons that the USFL did not sign other interested undergraduates who potentially posed the same legal threat as Walker. Simmons said if he had it to do all over, he would have signed at least one of those players, Willie Young, a 28-year-old military veteran who never graduated from college.