More openly than in earlier years, the president's budget debate with Congress now has to do not so much with the federal government's cost as with its role. He would diminish this, and not alone for fiscal reasons. The goal is in his budget message. Cut as he suggests, Mr. Reagan says, and "the result will be a leaner, better integrated, more streamlined federal government -- stripped of marginal, nonessential and inappropriate functions and activities, and focusing its energies and resources entirely on its proper tasks and constitutional responsibilities."

That is the vision that produces his acronymic graveyard. He would wipe out entire agencies and programs -- ICC, SBA, EDA, OPIC, UDAG -- and, yes, stop filling the SPR. The vision also leads him to his theme of sellinoff government assets -- the Naval Petroleum Reserves, more federal loans, the right to market future hydropower from the western dams.

These are the proposals not just of a determined president, but of an expert political dramatist. Many are sensible ideas. They have great symbolic resonance as well. They present only one real problem: they do less than their allure would suggest to reduce the deficit. The sentenced agencies and programs are mostly small; the asset sales would greatly improve appearances in the years when they occurred, but the basic problem of too little revenue to pay the bills would then recur, only the government would have less to its name.

Yet the president has put a tax increase and two thirds of all spending -- defense, which he would continue to increase, Social Security and interest on the debt -- off limits. What does he do? As he must, he returns much more than the budget themes would suggest to his familiar hunting grounds of social programs, aid to state and local governments and the government's own labor costs, the pay and benefits of federal employees. The big health programs, Medicare for the elderly, Medicaid for the poor, are now about a tenth of the budget and almost a third of what Mr. Reagan regards as the cuttable part. The budget documents show that by fiscal 1991 the president's proposals would reduce their combined cost by a seventh from the level to which it would otherwise rise. Spending on subsidized housing would likewise be cut by a third, the college student-aid programs by two-fifths. The deficit would be $105.2 billion smaller in 1991 under the president's plan than otherwise, the documents say. A third of this trimming would occur in health care, housing and student aid.

By the same standard, highway and other transportation grants to state and city governments would be down by a fifth by 1991. In real or after- inflation terms, total aid to state and local governments, already mch reduced in the Reagan years, would be down by another sixth. There would be sizable cuts in the cost to the taxpayers of the civil service retirement and health insurance programs as well.

None of these broad areas of federal expenditure cost is sacred or impossible to improve, and the president has made some provocative proposals. But surely these are not realms where the federal government does not belong, nor where its role should be diminished to the extent the president proposes. One of the things the federal government does is command resources and channel them to necessary public purposes for which they would not otherwise be spent, from the health care of the poor to the upkeep of the roads. The president, to avoid a tax increase, would do much less of this. He suggested in his news conference Tuesday night that he is merely trimming fat. We think he is into equity and bone.