Long ago Walter Lippman wrestled with defining that illusory, and largely lacking, quality: American leadership. Our rulers, he said, consist of random collections of people with only one common ingredient -- success. They could explain the secrets of success, but not how they got where they were.

As a group, he went on: "They have been educated to achieve success; few of them have been educated to exercise power. Nor do they count with any confidence on retaining their power. . . . They live, therefore, from day to day, and they govern by ear. Their impromptu statements of policy may be obeyed, but nobody seriously regards them as having authority."

Now, half a century later, after so many failed presidencies, an erosion of presidential authority, and public disappointment over governmental policies, an American leader beginning the most ambitious exercise of power in decades has a clear sense of purpose, a clear understanding of how he got where he is - and the most serious attention of the people.

The belief here is that the great majority of citizens wants Ronald Reagan to have authority to change the direction of government even if it affects them personally, and adversely. They recognize the correctness of his general diagnosis, although they are uncertain about his specific prescriptions for cures. Indeed, they felt the same way about Jimmy Carter's promise four years ago.

With the president's speech to Congress the other night, the Reagan Revolution now begins to assume concrete political form. We are witnessing potentially the most profound altering of the federal role since the New Deal, and thus the beginning of the sharpest political battle in at least a generation. Reagan now has a better than even chance of winning this fight. That prospect represents a dramatic altering of the recent odds in his favor -- in itself a rather astounding fact, given the capital's world-weary can't-be-done cynicism about how Washington really works.

Simply put, the essence of the Reagan approach is that America no longer can afford to do business the way it has been. From here on out, federal government support must be limited to programs of fundamental national priority. As Reagan himself put it in his speech, "spending by government must be limited to those functions which are the proper province of government. We no longer can afford things simply because we think of them."

Implicit in those words -- and others he uttered during his election campaign -- is the call for a radical reduction of the federal impact on all aspects of American life. At times Reagan sounds as if he were advocating a return to laissez-faire and the laid-back policies (meaning none) of a president he admires, Calvin Coolidge. But Reagan advocates more than a return to the freebooting days of yesteryear, and because he does his program stands a far better chance for success.

He and his people have gone to great lengths to assure Americans they are not trying to undo progress. They are, they say, committed to preserving the essence of the social programs that formed the heart of the New Deal and have become a permanent fixture of the country. Reagan says: "We will continue to fulfill the obligations that spring from our national conscience. Those who through no fault of their own must depend on the rest of us, the poverty-stricken, the disabled, the elderly, all those with true need, can rest assured that the social safety net of programs they depend on are exempt from any cuts."

In effect, Reagan says, he's not about to repeal the New Deal. By his definition those kinds of liberal programs that stem from the Franklin D. Roosevelt era remain "the proper province of government." From a practical political standpoint they also are supported by a majority of the American people, and Reagan and his top advisers know it even if some of their staunchest conservative backers blanch at the thought.

Reagan's program begins auspiciously for two other reasons. He has succeeded, in his initial presentation, in persuading people that that ensuing pain by and large will be felt by most citizens. (A glaring omission, one that will haunt the Reaganites, concerns keeping the tobacco subsidies in what appears to be a political payoff to pacify Jesse Helms, the rightwing Republican senator from North Carolina.) And Reagan strikes a chord among Americans everywhere when he stresses that government has gone awry.

People know that those who profit most from federal largess often are what Reagan calls the "array of planners, grantsmen and professional middlemen" instead of the citizens for whom the programs are intended. They also know, as virtually every president for a generation has been telling them, that the workings of government have become incredibly bureaucratic and inefficient. The Reagan team's example of problems with health and social services grants is all too true: "Over the years," their assessment states, "these programs have become ensnared in a staggering degree of waste, complexity, and bureaucratic overhead. The programs proposed for consideration encompass 437 pages of law and 1,200 pages of regulation. These programs administer 6,800 separate grants and approximately 24,000 grant sites. Once awards are made, over 7 million man-hours of state and local governments and community efforts are used just in filling out federally required reports each year. In addition, the nation supports over 3,300 federal employes to administer the grant programs proposed for consolidation."

Reagan capitalizes on the best possible national climate for change. That does not mean victory is assured or the political millennium has arrived. He faces as many problems as favorable prospects. Some are of his own making.

An astonishing tone of self-assurance runs through the Reagan proposals. They brim with optimism, with assertions of having the solutions. We have found the way. Follow us and all will be wonderful. Already the claims for complete success are overpowering. "Can we do the job?" Reagan asks. "The answer is yes." His people are no less convinced. Their promises are quite specific: their program will cut inflation in half, produce 13 million new jobs, lead to a much more robust growth trend of 4 to 5 percent a year, reduce tax burdens, increase private savings, raise the living standard of the American family -- and all simultaneously, all within the immediate golden future that beckons to us now.

They have left themselves no safety nets. Like Lyndon Johnson they have declared war on formidable foes at home and abroad and proclaimed victory in advance. They have thus set the stage for another great buildup of public expectations, and the peril of another great political disillusionment.

Still, Reagan's bold program is noteworthy, and perhaps historic. It forces Americans to examine comforting political myths -- the federal government in Washington is to blame for all our woes. It compels them to face hard realities -- the special interests that thwart the greater national purpose are made up of you and me. We all want more, and we've become accustomed to getting it from someone else, courtesy of far-off Washington. It puts both political parties on notice that they must redefine their basic principles and goals, and be prepared to defend them. It sheds light on the truth or falsehood of another political chestnut -- that state and local governments across American really are eager to get Washington off their collective backs and are capable of providing the services their citizens demand and expect.

So as the gong sounds and the great battle begins, here's one citizen who says let 'er rip. Only good can come from this kind of debate over national directions. It could even lead to a tempering and maturing of American society, to what Walter Lippmann called the creation of the "good society." Naturally the politicians, with their excessive rhetoric, turned that phrase into a call for a "Great Society." A modest approach is always more appropriate, especially in these times.