THE SENATE now has to vote on another bill not merely to raise the debt ceiling, but to move it above $2 trillion. That is a magic number, but these tend to be theatrical occasions anyway. Everyone understands that the bills are basically accounting devices, summaries of the accumulated deficits over the years, validations of decisions already knowingly made.

The House now sensibly tucks the required increase in borrowing authority into its budget resolution each year. But the Senate has developed an elaborate ritual in which senators offer amendments, mostly intended to distance their sponsors from the debt about to be registered. Speeches are made, votes are taken, points are scored. Then the amendments are quietly set aside, and the higher ceiling is agreed to.

This year, hwever, there is along with the usual posturing a more serious proposal. Put forward by Sens. Warren Rudman and Phil Gramm, it would, for the next four years only, tighten the congressional budget process to force down the deficit. The officially expected deficit for fiscal 1986, which begins today, is $171.9 billion. That figure would be enforced this year (itself a formidable task), then moved down in equal stages to zero by fiscal 1990. A target deficit would be set for each year, which the president could not exceed in his budget request, nor Congress in its budget resolution in the spring. The two houses would then be expected to live within the resolution in their authorization and appropriations bills that summer.

On Oct. 1, the first day of the fiscal year, the directors of the Office of Management and Budget and Congressional Budget Office would inspect these bills and pronounce whether they were within 5 percent of the target. If not, the president would have to make the necessary cuts, half from cost-of-living increases in so-called entitlements, the big benefit programs including Social Security, and half from the remaining spending programs including, prominently, defense. In each half, cuts would have to be spread evenly. The president would thus be bound by Congress' priorities; he could not exempt defense, for example. Congress would then have one more chance to comply with the target on its own; otherwise, the presidential cuts would be law.

No Congress can bind its successors, but this proposal would put a powerful forcing mechanism into the law without ceding to the president, as have other proposals, Congress' responsibility for spending. It would also open up to cuts both Social Security and defense, which together with interest on the debt are two-thirds of the budget and this year were the stumbling blocks in reducing the deficit. It contains the necessary caveats that it would not be binding in either recession or war. Members may want to refine it (should entitlements be half?), and we are not sure it should go on the debt-ceiling bill. The continuing resolution that will be required to fund the government beyond November might be a better vehicle. But why not try it? It offers discipline, and in the fifth year of this administration, that is badly needed.