Walter Cronkite should not have been sitting there playing Mr. Interlocutor to President Carter's Mr. Bones. President Carter has a press secretary. His name is Jody Powell.

If Carter wants to talk directly to the American public - and there was much to commend both the questions and the answers - then let those questions come through his press secretary. It simply is not a proper role for Cronkite or any other network journalist to perform.

At the end of the two-hour phone-in broadcast, Cronkite told Carter, "We (CBS) would be glad to sign you up again, Mr. President." I am sure that CBS would. I am sure the President and his media advisers would like to sign up again with CBS as well as audition for ABC and NBC.

And that is precisely the problem. CBS sought this role. It was not as if the White House notified the net-works, as it does in the case of news conferences, that the session was available for coverage by television and radio. CBS solicited the President's participation and then placed Cronkite in the role not of journalist but of master of ceremonies.

It is quite a different role than the one in which Cronkite asks for and is granted an interview with the President. That is a perfectly proper journalistic exercise.But on the telephone call-in, Cronkite was not functioning in the role of journalist. He was part of the White House propaganda machinery.

He did not think he was. But whether you listened to it on the radio or watched it on PBS, that conclusion was inescapable.

CBS should not have placed Cronkite in that fix. His great position of honor in American journalism derives specifically from what we perceive as his attachment from the stories he is reporting.

By his presence on the radio call-in show, that image of detachment has suffered. If it has not suffered in the public eye - and perhaps that is the case - then it suggests that the American people see nothing wrong in having him or other prominent television news commentators becoming part of the story rather than observers of it.

If so, then television news is in trouble. Carter is very slick and sophisticated about the use of the media, but especially so when it comes to television journalism.

What is so surprising about the network's seeming compliance in Carter's plan for them is that we have just come through a period, begining with John F. Kennedy, when Presidents have used the networks as it they were part of the Executive Branch.

Have we learned nothing from the excesses of that period? The Imperial Presidency fattened itself on many things, but primarily on free air time occasioned by the networks' fascination with the presidency and their seeming inability to deny Presidents virtually unlimited access to our home screens.

I do not say these things from a bias of the print media. The printed press has done its fair share in contributing to the mystique of the Imperial Presidency. But the polls tell us that the overwhelming majority of the American people get their information from television. Thus it is the networks, singly of jointly, that must sit down and try to determine how they can avoid being used as transmission belts - unquestioning and uncritical - for the views of those who occupy the White House.

Presidents will use any means at their disposal to get their views across to the American people. That is perfectly legitimate for them. But what the networks must do - and newspapers and magazines as well - is to keep from becoming an even greater part of the process itself.

"That is why I was so saddened by Walter Cronkite being up in a position that seemed foreign to everything he has come to represent in a long and distinguished career.