Ross Perot, who was unable to get into the presidential election debates, now is trying to get some of the free time the networks are giving his rivals. In a letter to CBS, the Perot camp cited the equal opportunity provisions of the Communications Act in asking for 2 1/2 minutes of free, unedited time from CBS-TV. President Clinton and Bob Dole were both granted that amount of time by the network, to be aired on October 21. CBS has not responded to the request yet.