SIGN OFF is billed, in its subtitle, as "The Last

Days of Television," but that is a misnomer. Edwin Diamond--recalled in Washington as a "media critic" on Channel Nine back 10 years ago when the phrase meant something--doesn't think television is in its last days but, like the rest of us, he can't see very clearly what its next days are going to be like. Cable, satellites, discs, cassettes, closed circuits, pay-per-view --these are all, he correctly notes, ideas whose time has come. The bad news--or maybe the good news--is that for some, it has come--and gone.

But this book contains a lively discussion of television in what Diamond calls its prime time--now. At MIT, Diamond and his colleagues in the News Study Group of the Department of Political Science have been conducting interviews and collecting and studying materials for 10 years. In that time--and as periodically reported in the interim studies called The Tin Kazoo and Good News, Bad News, Diamond has been analyzing all that material.

The earlier studies looked primarily at coverage of Vietnam, Watergate, the impeachment of Richard Nixon and the elections of 1968 and 1972. Good News, Bad News contained some excellent analysis of the 1976 election, the contest between Jimmy Carter and Gerald Ford which was, in retrospect, the first pure television campaign in our history (but not, alas, our last).

Now, however, the archives and studies at MIT have been, as Diamond says, "widened" to include other institutions and it is that wider analysis which is the basis for this book. Unfortunately, the MIT folks take that "News Study" handle very literally.

There is discussion here of network and local news programming--aptly called "Disco News" on the demonstrable proposition that the beat is often more important than the lyrics. There are treatments of documentaries, of religious programs and political preachers, of specific stories such as Three Mile Island and the Tehran hostages, of the coverage of economic issues and elections and an interesting if incomplete chapter on the traditional--and only slightly modified--reluctance to cover "scandalous" stories about prominent figures.

But except for an exegetic minute-by-minute study of sex on soap opera (a more useful barometer of social attitudes than the Study Group may believe), there is no analysis of what might be called non-news televsion-- Prime Time Entertainment in the industry term--in shaping our political and social attitudes. Elections may, in a narrow way, be affected by the way in which a David Garth or a Jerry Rafshoon shoots a commercial. But the determination that heavy viewers of prime-time drama believe crime to be far more prevalent than it actually is may be even more significant.

Diamond makes the point, and it is certainly worth citing as a major factor through the primaries of 1980, that the constant stress in news programs of the hostage crisis (". . . and that's the way it is . . . the 143rd day of captivity") made Jimmy Carter's failure to discuss the issues of the day an almost patriotic duty (what if the news broadcasts had concluded with ". . . and that's the way it is . . . the 143rd day of double-digit inflation"?).

But this book would be a more complete study if its ambit included more than the news/public affairs side of TV. We are told, for instance, in a discussion of "endorsement commercials, that the forces of Senator Edward Kennedy switched advisers before the New York primary, and that the new team came up with some spots featuring actor Carroll O'Connor. But there is no discussion of why this one actor was chosen over others, only that he was "better known to television viewers as Archie Bunker."

But the point, of course, is that O'Connor is known to the audience only as Archie Bunker, and that is why he was chosen for the commercial. Does anyone think Robert Young would be recommending the therapeutic effects of decaffeinated coffee if he had gone on playing a goofy father and not become the nation's best-known doctor? For that matter, would John Wayne have received a medal as a "great American" if he had played rustlers, renegade Indian agents and Nazi colonels instead of cowboys, cavalrymen and U.S. Marine sergeants?

It is in this complex area--where the viewer exchanges the chaotic reality of his own life and experience for the ordered and much more "realistic" realty of prime-time television--that many social (and, one assumes, political) attitudes are shaped and changed. If the Mary Tyler Moore character some years ago revealed she was "on the pill," why not a few million viewers? Can we guess how many teen-age car crashes might have been avoided if there had never been a Dukes of Hazzard? For that matter, would Ronald Reagan have become a successful candidate if he had played the villains' roles during his time in Hollywood?

Diamond touches on this phenomenon of life's imitating art in his discussion of TV news coverage of the 1980 campaign. Even without placing it in the broader context of "entertainment," this book is worth reading and pondering for these sections alone. The question of how voters finally perceived George Bush during the primaries of that campaign (preppie by style; Reaganite by content) is fascinating, and so is the look at the hype given by journalists to the John Anderson campaign.

Diamond concludes by saying "we get the press we deserve," by which he means that the media reflect the society at any given time. I only wish he had devoted more time to the question of whether television doesn't shape that society in large part, and then reflect it. We can look forward to the next MIT study, and Ed Diamond's next report.