FISCAL AUSTERITY is one thing. Calling the government to a halt is something else. In its coming consideration of the budget, the Senate should keep in mind the differences. We are all discovering that it is difficult to live in a time when all the chickens are coming home to roost. The Senate is caught between the desire to increase defense spending and the conviction that government programs in general must be curtailed. All the chickens -- and a few vultures -- of the past two decades' governmental spending policies are alighting at the same time, and one cannot blame the senators if the impulse is to take cover.

But before they do, it is really essential that the government be kept in business -- at least those programs for which statutory entitlement exists -- while an orderly process of dismantling some of them is set up. This means that 1980 funds for food stamps and black-lung benefits, for example, need to be assured -- now. In addition to the obvious obligations of decency involved here, there is the practical fact that the 1981 debate should not be conducted under the deadline created by the imminent suspension of these programs.

After these emergencies have been taken care of, the 1981 decisions can be given the serious thought they deserve. These decisions have historic importance, for it is clear that now is the time to sort out which parts of our budgetary inheritance to maintain, ane which to discard. A massive change has occurred over the past 10 years in the distribution of federal resources, largely away from defense and toward payments to individuals.Most of the decisions that contributed to the change were made piecemeal: they were political compromises, and their implications were rarely examined with care.

For example, in 1972 the indexing of Social Security benefits was first enacted, and a one-time 20 percent benefit increase set in place to take effect close to election day. The political heat was on; Richard Nixon was running for reelection and was under attack for doing too little for the elderly. The rush to pass and sign the bill was so great that a drafting error was made that resulted in calculating the inflation index twice. It took five years until the political will was mustered even to correct the error. Nobody was pushing for the change.

The budget got into its present shape because the electorate seemed to be communicating with the federal government as hundreds of interest groups, more worried about individual pieces of the action than about the overall future of the enterprise. But enough time has elapsed for the shortcomings of some of these programs to have become clear. The Senate's job is to decide which ones we can live with and which we cannot. It cannot be expected to make these decisions wisely in the increasingly hysterical atmosphere that will be generated if the need for 1980 funds for essential programs is not dealt with first.