George Anderson, trainer of the Oakland Raiders, has been found innocent of charges that he gambled on National Football League games, placed bets for other employes of the team or provided inside information to gamblers about player injuries, a league spokesman announced yesterday.

The NFL said it had thoroughly investigated the accusations before clearing Anderson.

The charges originated in a statement made 10 years ago by a paid public informant and revealed Oct. 18, 1981, in a New York Times story.

NFL Commissioner Pete Rozelle said his security department had not found any substantiation of the charges. Rozelle said Anderson admitted having bet more than 10 years ago on events other than football through an illegal bookmaker and of having socialized with another bookmaker.

Rozelle said the league had discussed those activities and associations with Anderson, and cautioned him about future involvement.

In other football news, the Baltimore Colts' new coach, Frank Kush, will return to Arizona State for a preseason game against the Atlanta Falcons Aug. 21, a team spokesman said. Kush was fired by the university in October 1979 after accusations he tried to cover up allegedly punching punter Kevin Rutledge. Rutledge filed suit against Kush in 1980 and a jury ruled in Kush's favor. The Colts open their preseason with the Aug. 7 Hall of Fame Game against the Minnesota Vikings at Canton, Ohio. The rest of the preseason schedule: Aug. 14--New York Giants, Aug. 28--at Pittsburgh, Sept. 4--at Chicago. . . . Paul Dietzel, under fire because of a losing record and developing financial problems, is out as athletic director at Louisiana State University. The Board of Supervisors voted to reassign him as assistant to the LSU president "for the development of projects and programs" until his contract runs out in July 1983; he will keep his salary of $66,000. No word on who would replace him as athletic director.