WHO RULES AMERICA? The question always fascinates, and always will. Nor is the answer obvious, even if you rephrase the question to, who runs the United States government? It was easier to answer half a century ago, when President Coolidge had one executive secretary and three other assistants on his payroll, or when Franklin D. Roosevelt avoided the tension that now plagues every administration between the State Department and the national security adviser by running foreign policy himself, personally. Now we speculate about who is controlling the flow of information to the president, who is writing his talking papers, who determines which options he will choose between -- and we do so not only about the 71-year-old incumbent but about his physically more vigorous and apparently more alert recent predecessors.

So one answer to the question, "Who governs?" is: a great many people. Reagan's Ruling Class, a book written by two of Ralph Nader's staffers, recognizes this by profiling fully 100 people. The authors, Ronald Brownstein and Nina Easton, readily admit that others will cavil at some of their choices and decry some omissions. Why, for example, do we get profiles of two members of the Legal Services Board, but nothing on Robert Carleson, a White House official who, according to Patricia Harris, seems to be dictating social welfare policy? Why is there nothing on Richard Darman, the assistant to James Baker identified as a kind of devil by many in the New Right? We get more on the Agriculture Department than we probably need, and although there is a nasty controversy going on at the Government Printing Office, is it all that important to the rest of us?

Having said that, I must go on to say that this is a useful and often enlightening volume, which tells us a great deal of what we should know about many of the top appointees in the federal government. If the book falls short of its goal, it is partly because that goal is very ambitious indeed. Describing an administration is like pinning down a tomato seed; a number of the book's subjects -- Alexander Haig, Norman Ture, Murray Weidenbaum -- have already disappeared. Brownstein and Eaton don't try to tell us much about these people personally, though they give a few personal impressions of the 57 appointees they interviewed, but they do provide information about their professional backgrounds which goes far beyond mere r,esum,es. While there is good reason for doubting that experience working, say, for a corporation biases a person as much as the authors suggest, it is certainly true that we are all the product of our experiences, and where one comes from provides at least some clues as to where, in office, one might go.

Reagan's Ruling Class tries to sketch out the major issues each of these appointees will handle. Undoubtedly specialists will find some of their treatments deficient, and certainly many readers -- not all of them Reaganites -- will find them irritating. The discussion of the administration's arms control policy has a sternly disapproving tone; you don't have any doubts about where the authors stand on occupational health and safety issues. The authors note carefully, and with evident distaste, the smoking habits of Malcolm Baldrige and Robert Burford. But writers are under no obligation to be nonpartisan, and the bias of the book is clearly advertised. I can't vouch for the accuracy or fairness of all its portrayals -- is there any single person who can? -- but those I think I know something about make sense. The effectiveness of appointees like David Stockman, Drew Lewis, and John Lehman comes through. And the authors have made it clear to anyone who can read between the lines who some of the buffoons of this administration are: Robert Nimmo of the Veterans' Administration, Raymond Peck of National Highway Traffic Safety.

The strength of Reagan's Ruling Class is in its specifics rather than its generalizations. The title rankles: Do all these people really come from the same class? In his press conference publicizing the book, Ralph Nader emphasized the personal wealth of its subjects, and in his introduction he calls them "evangelists of corporatist political ideology." This would be demagoguery were there any sizeable segment of the electorate inclined to believe it. Our history is full of examples of wealthy men who took the side of reform -- the Roosevelts, the Kennedys -- and many of the Reagan appointees who have been most effective in cutting programs for the poor -- David Stockman -- are people whose personal financial status is quite modest. And of course there is nothing wrong with staffing a government with people who have achieved great success in life -- which often means people who have made a lot of money.

Indeed, I would critcize the Reagan administration for something like the opposite failing. Only 17 of the 100 appointees here, by my count, come from corporate America, and only a few of these -- Treasury's Donald Regan, Energy's W. Kenneth Davis -- were really major movers and shakers at the corporate level, far fewer I suspect than in most Republican administrations. Nor are there all that many from Main Street. I count some 27 who came to office with recent deep roots in local communities across the nation, and they are a mixed lot -- some highly effective like Drew Lewis, some distinct embarrassments like Raymond Donovan. Most of the subjects of this book -- 56 of the 100 -- I would characterize as mandarins, men and a few women who have made their livings studying government or lobbying it in think tanks or academe or Washington law firms. Many staffed, at slightly lower levels, for previous Republican administrations; only a few have ever held elective office.

Nader would claim that these people are the slaves of the corporations whose causes they have on occasion championed. I think a greater danger is that they might be the slaves of stale theories. Their ideas are never tested by the experience of life in a community that Main-Streeters get: service on charitable boards, negotiations and working relationships with union leaders, contact with people in a wide variety of businesses and professions, concern about local schools. In a way these Reaganite mandarins are the right-wing counterpart of Nader's Raiders: cut off deliberately from local roots, focused on ideas, convinced of their righteousness. No wonder they don't like each other.

Mandarins like to think it is possible to run things, and sometimes it is. David Stockman's budget cuts did influence the conduct of government in many ways. But often people in charge change things only at the margin, or just keep the system going. The authors say that William French Smith "would be assured a seat in any room where the few hundred men and women who run the country were gathering." You can see the Naderites itching to get into that room, where by some mischance their adversaries are sitting now. What they don't understand, even as they provide us with fascinating and useful information about those people, is that Reagan's ruling class only runs the government and seldom, unless in war, really rules.