PRESIDENT REAGAN'S theory of the federal budget seems to take the year 1960 as the point after which things began to go wrong. That, certainly, is the thought with which he opened his speech on economic policy last week, and that seems to be the controlling view as his administration initiates the most powerful challenge of the past generation to the conventional budget. American politics is now coming into a profoundly interesting time as the traditional ideas about public spending are suddenly ordered to stand up and account for themselves. That's a highly useful exercise, and there have been more than enough mistakes of public judgment over the past 21 years. But it would be inane to succumb to the myth of the 1950s as a better, more orderly time for Americans, from which they have slipped through self-indulgence and inflation.

There is now an implication that Eisenhower policy is the new administration's intellectual point of reference as it embarks on this daring attempt to rewrite the budget. Perhaps Mr. Reagan's challenge is not only to Mr. Carter's last budget as it stands, but to the 21 years of social initiatives that have transformed it. Certainly this is an inference that can be drawn from much of the diffuse complaint about the social programs and about increased federal involvements in people's lives generally. But are Americans really worse off now than then? How would you measure the change? And what did the federal budget have to do with? We need to have these things straight if we are to know what we are trying to achieve in this reordering of budget priorities and commitments.

In fact, Americans are a great deal richer than they were in 1960. Per capita, after federal taxes and after inflation, the average income is up by two-thirds. But money is hardly what counts in the end. One basic measure of the standard of living is life itself. The average American life expectancy now is nearly 74 years, more than four years longer than in 1960. Part of it has nothing directly to do with money; physical exercise, for example, is now in fashion. But much of the progress reflects the public money pumped into public health, not only into the hospitals and research laboratories, but into those wildly expensive sewage treatment plants, and into the community action programs that showed isolated and ignorant people how to get health care. The infant mortality rate is always a good indicator of a country's social organization. After a long period of stagnation, it began moving rapidly downward again in the late 1960s. Its relationship to Medicaid and food stamps is beyond argument. Before you decide that food stamps are too expensive, consider carefully what they buy.

Surely another basic element in the standard of living is access to education -- in this country, the key to equality of opportunity. In 1960, there were fewer than 4 million students enrolled in colleges and universities. This year, there are more than 12 million. That couldn't have been accomplished without federal money for both the institutions and the students. Perhaps some of that aid can now be scaled down a little. But before you take your pencil to that part of the budget, remember that it has brought opportunity for many millions of young Americans to whom, in an earlier generation, it would have been foreclosed.

The list can be carried on at length. Housing standards are higher. Pensions are more generous, and personal economic security in general is better protected. For most people, working conditions have improved. None of these things was accomplished solely with federal money, but none of them would have been likely without it.

There's a difference between history and nostalgia. The 1950s were no halcyon time of public wisdom and private dilligence. The United States in those years was a society under strain. Inflation was held in check, but at a cost of three recessions in eight years and exceedingly slow growth of incomes. The question isn't whether the country can do that again, but whether it can't do better.

It's true that Americans are living currently beyond their means. It's true that the country is going to have to cut down a little, beginning with the federal budget, to restrain inflation. But it's also true that the federal budget is inseparable from the American standard of living. If it's the last 21 years that are under challenge, there's an obligation to remember what those 21 years have brought. By no means can all of it be measured merely by money. This ought to be the starting point of understanding in the administration's effort to bring the budget under control.