ONE EVENING THREE YEARS AGO, when I was writing Jimmy Carter's speeches and (an unrelated fact) his lead over Gerald Ford in the polls was rapidly vanishing, I was buttonholed by a disgruntled Democrat who loudly blamed all the campaign's woes on Jody Powell. Somewhat to my surprise, for Powell and I had experienced certain conflicts by then, I found myself defending the press secretary. "It's Carter," I said wearily. "Good or bad, win or lose, this campaign is 99 percent Carter. The rest of us are just along for the ride."

That remains my view of Carter's administration: good and bad, it's all Carter. Thus, I was not surprised when he recently undercut his politically effective "down-from-the-mountain" speech with his politically disastrous Cabinet massacre.It was what, back in the campaign, we used to call "pure Jimmy," and the sad fact is that all the Jody Powells and Jerry Rafshoons in the world can't save Jimmy Carter from himself.

These thoughts are occasioned by the publication of Michael Medved's The Shadow Presidents, an examination of one influential presidential adviser in each administration, from Lincoln's to Carter's. It is a readable, well-researched book, good popular history, but my main reaction to it is a sense that we have tended in recent years to overrate, overexamine and overglamorize the men around our presidents.

Presidential aides are often colorful, and they make fools of themselves with amazing regularity, but how often do they really matter, except to job-seekers and journalists? Obviously they do sometimes, when the chemistry is right, as when Colonel E. M. House pushed Woodrow Wilson toward World War I, or when Clark Clifford edged an uncertain Harry Truman toward the "give-'em-hell" campaign style that won the 1948 election.

But more often the presidents' men are quite replaceable, and their importance is exaggerated by themselves and also by writers who have found them more approachable and more understandable than the presidents they serve. Medved argues, to take one example, that John Kennedy might never have been president without Ted Sorensen's writing skills. Perhaps so, but I strongly suspect that if Sorensen had not existed Kennedy would have invented him, just as Lyndon Johnson would have found another Bill Moyers to reflect a certain side of his personality.

Presidents tend, for better or worse, to get what they deserve. If there is any clear lesson from all the Watergate memoirs, for example, it is that the sort of aide who might have saved Nixon from his folly would never have gotten onto Nixon's staff in the first place.

These reservations are not intended as criticism of Medved's book which, as I said, is well done. Medved, co-author of What Ever Happened to the Class of '65?, tells us that in 1970 he was the speechwriter for a Senate candidate and found that "an extraordinary interdependence developed" between them. He therefore became curious, he says, to find out how much of America's history had been made by its presidents and how much by its "shadow presidents."

He decided to start with the Lincoln administration, and thus "rescue from obscurity" various aides to 19th-century presidents. It could be argued that several of those aides richly deserved their obscurity, although I found the book's political minutiae to be one of its fascinations. For example, trivia fans, do you know what president had an enthusiastic hashish smoker on his staff, or what president had a gangling, slum-bred young secretary who proceeded to marry his (the president's) daughter, change his name and become a multi-millionaire: The answers are Lincoln and Garfield; see the book for details.

The most important chapters, of course, deal with historically important figures. The role of President Grant's aide, Orville Babcock, in the Whiskey Ring scandals casts interesting light on Watergate, and Medved's summary of the Wilson-House relationship is quite fascinating. His chapters on such recent notables as Clark Clifford, Sherman Adams and Bill Moyers add interesting new details on those much-written-about figures without altering our basic understanding of them. Sherman Adams, for example, hinted to Medved that his investigation into CIA spending may have led the CIA to "set him up" in the Bernard Goldfine affair.

Medved has interesting chapters on Nixon's H. R. Haldeman, whom he views with sympathy as a man far over his head in the political waters, and Ford's Richard Cheney, whom he portrays admiringly as the very model of a smart, discreet, loyal presidential aide. In praising Cheney, Medved correctly notes that the most effective White House aides have always been those who avoided publicity like the plague.

Which brings us to the current White House where two dominant staff figures celebrated their arrival in Washington by posing for the cover of Rolling Stone dressed as Butch Cassidy and the Sundance Kid.Various of Carter's close aides have harmed him by overt acts, others by quiet mediocrity. Medved focuses on Hamilton Jordan, and to a lesser extent on Powell, but he does not tell us anything new about their misadventures. Rather, he ventures the theory that the failures of the Carter staff resulted because they and Carter ignored four rules: 1) A president should have a chief of staff; 2) that top aide should have done something in his adult life besides work for that president; 3) presidential assistants should avoid publicity; 4) presidents should not be emotionally dependent on their top aide.

Those are fine, logical rules, and I am glad to see that the Carter White House is now following two of them, but I do not expect to live long enough to see any president follow all of them.