Everybody knows there is a private sector and a public sector in the economy. But there is also - though little recognized - a private sector and a public sector in American politics.

The tension between these two sectors of the polity lies behind the so called tax revolt. It explains many other puzzling features of national life, including the rise and relative ineffectiveness of such leaders as President Jimmy Carter and Gov. Jerry Brown of California.

I borrow the distinction between the private sector and the public sector of the polity, along with much of the accompanying argument, from a series of recent articles by Prof. Samuel Beer of Harvard. In Prof. Beer's categorization, the private sector of the polity includes the voters in general, and most of the traditional interest groups: business, labor, farmers, minorities and the various national regions.

The interplay of those private interest groups has in the past been the determining feature of national policy. The private interests acted upon government to produce the New Deal of Franklin Roosevelt, the stand-pattism of the Coolidge-Hoover years, the New Freedom of Woodrow Wilson and the national policies of the 19th century.

But since the administration of Lyndon Johnson, and especially in the last five years, there has grown up an increasingly large interest group that is not private in origin but lives off the government. Its beating heart, is the federal bureaucracy. It also includes various professionals in the businesses, laboratories and universities dependent upon the federal government. It extends to the vast network of officials working for the states, counties, cities and other municipalities.

Though not formally recognized as individuals, this public sector has acquired a certain fame, or notoriety, under various collegial names. The military-industrial complex is the most famous example. There is also the health syndicate, the educational establishment, the welfare bureaucracy, the highway lobby, environmental mafia and so forth.

These government professionals are important because of their central role in the creation of policies and programs. Whereas such legislation as the anti-trust acts or the Social Security Act or even the first civil-rights acts derived from constituency blocs in the private sector of the polity, most new legislation emerges from the public sector of the polity.

Prof. Beer cities the case of the Community Mental Health Facilities Act of 1963, which came not from any public clamor, but through the initiative of a single doctor. In fact almost all recent legislation - whether in health, housing, urban affairs, race, welfare, poverty, education or communications - has been initiated and designed and lobbied and administered by the government professionals rather than by the private interests.

The immediate upshot of all this is that the voters, and their interest groups, are constantly being asked to support what seems like an endless proliferation of programs they don't understand or like. To most of the electorate, government comes to seem both incomprehensible and irresponsible.

It is natural, in these conditions, for the private sector to turn to political candidates who come on as being against the system - candidates like Jimmy Carter and Jerry Brown. But however well intentioned and bright, inexperienced outsiders cannot master the system. The governmental reforms proposed by both President Carter and Gov. Brown have turned out to be irrelevant if not jejune, and in office both men have quickly lost credibility.

At that point the voters go for arbitrary measures of control - like Proposition 13 in California, and the crop of copies that have been springing up all over the land. But it seems very doubtful that putting arbitrary limits on spending can meet the legitimate demand for responsive and comprehensible government any better than putting outsiders on the inside.

On the contrary, the governmental monster can be tamed only through the deliberate application of carefully conceived policies by knowledgeable persons. The professional state that was so sedulously prepared by Lyndon Johnson can be dismantled only by a president of comparable skill, energy and knowledge of the system.