The Federal Trade Commission yesterday investigated the restricted television coverage of this weekend's National Football League playoff games for possible antitrust violations by the networks, but concluded that the schedule had been ordered by the NFL, which is exempt from antitrust prosecution in the broadcasting field.

In effect, the FTC was investigating to see if the football-watching public was being deprived illegally by CBS and NBC of the right to "channel switch" from one playoff game to another. Under the schedule ordered by the NFL, viewers in any place in the country can get only four of the eight weekend playoff games on their TV screens--two on Saturday and two on Sunday--so the networks never are in head-to-head competition.

Val Pinchbeck, the league's director of broadcasting, said the restricted television schedule was picked because "we felt it was the best business decision for us. We can maximize ratings that way." The TV networks were reported to have been upset by the NFL decision.

FTC officials said they are not allowed to comment on nonpublic investigations. FTC sources said, however, that the entire commission approved the probe because it involved the media and a possible First Amendment issue.

The FTC investigation was triggered early this week when its antitrust lawyers noted that the public would not be able to watch the full plate of playoff games. Instead, CBS was given an early slot for its two Saturday afternon games, while NBC got the late afternoon position. On Sunday, the networks reversed, with NBC doing the early games and CBS the late ones.

With the networks running in different time slots, the TV-bound fan cannot shift from a dull game to a more exciting one or, heaven forbid, switch from a commercial on one channel to live action on another. The NFL's Pinchbeck, however, said the networks can cut in from one game to another in their time slot, making sure the fan sees all the important action.

Had the networks arranged the schedule this way, it is likely there would have been a violation of federal laws against conspiring to restrict competition. But because it was ordered by the NFL, which was given a special exemption to deal with the television networks and to control TV coverage of its games, the restricted coverage breaks no law.