Catholic University apparently violated NCAA rules because defensive back Chris McMahon's senior season last year constituted his fifth season of intercollegiate football competition, CU Athletic Director Fred O'Connor said yesterday.

O'Connor said he became aware of the violation, which could result in Division III CU forfeiting its five victories last season, on Tuesday, when he was notified by the Eastern Collegiate Athletic Conference that an unidentified person had reported it to the NCAA.

McMahon, who attended Gonzaga High School, transferred to Catholic from Holy Cross after his sophomore year. McMahon played on the junior varsity as a freshman at Holy Cross and played in five games as a sophomore before contracting mononucleosis. He transferred to CU and played three seasons. Last season, he intercepted 13 passes and was a Division III all-America.

The ECAC is trying to determine whether CU officials were aware at the time that last season was McMahon's fifth . The facts of the case are in dispute.

According to O'Connor, who became athletic director a year ago, McMahon asked Coach Joe Pascale (who was not rehired after the season) to investigate if he was eligible, and Pascale subsequently told the athlete that he was. O'Connor said that McMahon's eligibility had been established before he became athletic director.

Pascale said yesterday that he asked O'Connor about McMahon's eligibility and submitted two eligibility lists for O'Connor's approval. "He didn't tell me anyone was ineligible. The list went through," Pascale said. "It's his responsibility being the executive athletic administrator. He told me he was the boss. I did everything I was supposed to do."

Pascale said he asked O'Connor about petitioning the NCAA for a waiver because of McMahon's illness as a sophomore. O'Connor denied that Pascale sought the waiver, which the NCAA usually grants when an athlete is injured or becomes ill and plays in 20 percent, or less, of a team's games. An NCAA spokesman said if McMahon had played in even four games at Holy Cross, he would have been ineligible for a waiver. McMahon was unavailable for comment.