PRESIDENT REAGAN'S budget bill, with its gigantic catalog of spending cuts, has now been passed by Congress and is on its way to the White House. Final passage of his tax bill is similarly assured, probably within the next several days. The Reagan economic program is no longer future, conditional and speculative. It's here.

This moment culminates a long turn in the direction of American politics. The earlier stages of it were the declining confidence among the Democrats in their own purposes, and the immobilization of the last administration as each of its good intentions collided with all the others. It was clear last winter, in contrast, that the Reagan administration enjoyed the large tactical advantage that goes to people not much troubled by inner doubts.

The great surprise of the spring and summer has been the extraordinary vigor and audacity of the Reagan White House. To have committed itself to the rapid passage of such complex legislation was, by any measure, extremely daring. There were probably not many people -- certainly not ourselves -- who expected more than a much compromised and delayed outcome. As a feat of legislative engineering, the victory is spectacular. It is difficult to think of another bill that has touched as many different subjects as kthe budget reconciliation bill that Congress completed on Friday -- less than three months after it began.

But for all of the administration's skill and stamina, it has been able to move with such speed only because nearly everyone in plitics, its adversaries as well as its friends, recognizes a deep and widespread sense of public exasperation with the way things had been going -- with, as the president calls it, the "economic mess." But what, exactly, do people mean by the economic mess?Most of the country remains very prosperous.

Many people mean inflation, when they speak of the mess. Many also mean slow economic growth, and the failure of incomes and living standards to rise as fast as they used to. For some people, particularly in the steel and automobile towns, the term "mess" is an expression of resentment against rising foreign competition. The Carter administration was destroyed by its inability to make firm choices among these conflicting claims.

In theory, the Reagan program is going to remedy all of these various kinds of distress without requiring choices among them. In practice, it won't be so simple. As the Reagan program now stands, it is indeed likely to lead to a faster expansion of business and employment -- particularly with the force of rising defense spending behind it. But the prospect of bringing down inflation at the same time is, to put it midly, uncertain. Those two things, rapid growth and declining inflation, have never been accomplished simultaneously before.

The greatest virtues of the Reagan program as it is embodied in thse two enormous money bills, have little to do with money. These bills dispel the atmosphere of futility and stalemate that gathered around American economic policy throughout the 1970s. That's a healthy change, for reasons that run well beyond economics. These bills dramaticaly reassert political control over much that previous presidents, with many shrugs, had abondoned as uncontrollable. That's equally healthy.

But as a statement of social policy, the tax bill in particular, with its implication of widening differences among economic classes, falls well short of the standards that this country's traditions had previously established. The Reagan administration argues that these bills will generate a wave of prosperity bringing greater benefit to even the most impoverished Americans than direct government intervention ever did. That's a fair test by which to judge the period that begins with the signing of this legislation.